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Integration issue with PyObjC and TKinter
Question: The following simple code:
from PyObjCTools import AppHelper
import AppKit
import Tkinter
class App(AppKit.NSApplication):
def finishLaunching(self):
self.root=Tkinter.Tk()
_=App.sharedApplication()
AppHelper.runEventLoop()
yields the following exception: `Python[23717:d07] -[App _setup:]:
unrecognized selector sent to instance 0x105d05340`
What am I doing wrong?
Answer: I don't think you can mix Tkinter and Cocoa toolkits so interchangeably.
`self.root` is an attribute on the class `App`, which inherits from
`AppKit.NSApplication`. My guess is that the `Tk()` call returns a pointer
that is then passed to the Cocoa frameworks, but points to a Tk data structure
that it can't understand. Also, both Tkinter and PyObjC need their own
eventloop; I'm not sure if you can even mix the two (though I've never tried).
My recommendation would be to use one UI toolkit or the other, but not both.
|
How to Calculate the number of days in the year(s) between 2 dates in python
Question: I'll try to explain what I need with an example:
date 1 : 1 january 2000
date 2 : 17 november 2006
-> now I want to know how many days there are between date 1 and date 2 in the year 2000, 2001, ..., 2006 so I need something that returns something like this (doesn't matter if it's in a list or something):
2000: 365, 2001: 365, ..., 2006: 320
I've looked for something like this on the internet but that only turned up
ways to calculate the number of days/months/years between 2 dates
kindly regards,
Daquicker
Answer: hm, try something like this:
import datetime, calendar
date1 = datetime.date(year1, month1, day1) # month and day are 1-base
date2 = datetime.date(year2, month2, day2)
days_in_first_year = (datetime.date(year1,12,31)-date1).days
days_in_last_year = (date2 - datetime.date(year2, 1, 1)).days
if year1 != year2:
n_days_list = [days_in_first_year]
for year in range(year1+1, year2): n_days_list.append(365 + (1*calendar.isleap(year)))
n_days_list.append(days_in_last_year)
else: n_days_list = [days_in_first_year + days_in_last_year]
haven't tested this, might be some off-by-one errors; make sure it does what
you expect.
edit: correct the boundaries of the range() call, correctly handle year1 ==
year2
|
Threading issue with instance variables
Question: So it seems I'm misunderstanding some basic stuff about Python. Passing an
instance variable into a function should only pass a reference to the object
itself, so in case the object is immutable doing something like `self.var =
"something"; foo(self.var)` shouldn't change self.var if foo assigned a new
value to the variable - so long everything's fine and as expected.
But now consider this:
import threading
class Test():
def __init__(self):
self.lock = threading.Lock()
self.arg = "arg0"
def foo(self, i):
with self.lock:
threading.Thread(target=lambda: bar(self.arg)).start()
self.arg = "arg" + str(i)
def bar(arg):
import time
time.sleep(1)
print("Bar: " + arg)
if __name__ == '__main__':
t = Test()
for i in range(1, 6):
t.foo(i)
I create a thread object with a reference to the current string and afterwards
update it - which the thread shouldn't see. Thanks to the lock the next thread
also should only start after the update - so while I can't make any
assumptions about the sequence in which arg0-5 will be printed I'd assume
every arg should be printed exactly once. But I get the following output (Win7
x64, python 3.1 x64)
Bar: arg0
Bar: arg2
Bar: arg2
Bar: arg5
Bar: arg3
Edit: Okay after typing this up, I had the glorious idea that probably the
lambda expression isn't executed when creating the thread but later on, which
would explain the behavior, so the simple workaround would be to just create a
local variable and use that. Well - now that was fast help by SO ;)
Answer: Since I noticed I still hadn't answered that one, here we go:
The lambda creates a closure to `self` but not to `self.arg` itself, which
means when we later execute bar we access the newest value and not the one at
lambda creation time.
|
building executable using python,vtk and py2exe
Question: Is it possible to create a binary executable with py2exe for vtk?
Could someone provide a minimum working example or at least some hints? Py2exe
is not necessary. If there is a working solution on other similar programs
(bbfreeze etc) I am intrested too.
Answer: This example uses py2exe. Use packages to add any referenced libraries and
options includes to add dependencies. I am not too sure about the exact
semantics and I reached this stable configuration after much trial and error.
Hopefully, you can use this as a template to go ahead.
from distutils.core import setup
import py2exe
import modulefinder
from iso8601 import iso8601
setup(name='exeExample',
version='1.0',
description='Exe example using py2Exe',
author='Urjit Singh Bhatia',
author_email='person@user.com',
packages=['example', 'someLib'],
console=['src\\a.py',
'src\\b.py',
'src\\c.py',
'src\\d.py'],
options={"py2exe":{"includes":["someLib","csv","iso8601","pymssql","uuid","decimal","urllib2","traceback","re","_mssql","os"]}}
)
Keep in mind that options, includes sometimes need to be nested. That means,
if pymssql here uses _mssql, it was giving me an error saying that _mssql was
missing, so I had to explicitly go and add that as a dependency.
I hope someone can improve and explain.
Edits: 1\. Added imports. 2\. Simply running this creates a folder called dist
where you will see the exe(s) and the dependencies.
|
Does haskell have a splat operator like python/ruby?
Question: In python / ruby (and others, I'm sure). you can prefix an enumerable with *
("splat") to use it as an argument list. e.g in python:
>>> def foo(a,b): return a + b
>>> foo(1,2)
3
>>> tup = (1,2)
>>> foo(*tup)
3
Is there something similar in haskell? I assume it wouldn't work on lists due
to their unknown length, but I feel that tuples ought to work. Here's an
example of what I'd like:
ghci> let f a b = a + b
ghci> :t f
f :: Num a => a -> a -> a
ghci> f 1 2
3
ghci> let tuple = (1,2)
I'm looking for an operator (or function) that allows me to do:
ghci> f <op> tuple
3
I have seen <*> being called "splat", but it doesn't seem to be referring to
the same thing as splat in other languages. I tried it anyway:
ghci> import Control.Applicative
ghci> f <*> tuple
<interactive>:1:7:
Couldn't match expected type `b0 -> b0'
with actual type `(Integer, Integer)'
In the second argument of `(<*>)', namely `tuple'
In the expression: f <*> tuple
In an equation for `it': it = f <*> tuple
Answer: Yes, you can apply functions to tuples, using the
[tuple](http://hackage.haskell.org/package/tuple) package. Check out, in
particular, the
[uncurryN](http://hackage.haskell.org/packages/archive/tuple/0.2.0.1/doc/html/Data-
Tuple-Curry.html) function:
Prelude Data.Tuple.Curry> (+) `uncurryN` (1, 2)
3
|
Retrieve plain text JSON, insert into JavaScript
Question: I have a URL `http://myapp.com/get_data` that returns an `application/json`
`Content-Type`. When I browse to that URL, I'd get a plain-text JSON array in
my browser window
[[key, value],
[key, value],
[key, value],
...]
I also have a JavaScript function that expects data to be in JSON array format
function process_data() {
var data = // give me more data in JSON array format...
}
How do I make my JavaScript browse to `http://myapp.com/get_data` and assign
the resulting JSON array into the `data` variable inside `process_data()`?
I'm new to JavaScript (coming from a Python background) and I would appreciate
if you can suggest solutions that use the core JavaScript library. Solutions
using other libraries are welcome also, preferably those that are considered
best-practice.
# UPDATE
It appears I wasn't clear on my question. Let me provide an example from
Python. After doing the necessary imports, I can do something like
url = "http://myapp.com/get_data"
page = urllib2.urlopen(url)
page_source = page.read()
This time, `page_source` is already a Python `str` object that I can easily
play with, assign to other variables, etc. If I could mix Python and
JavaScript together, for the context of this question, I want to do something
like
function process_data() {
url = "http://myapp.com/get_data"
page = urllib2.urlopen(url)
page_source = page.read()
var data = convert_str_to_JSON(page_source)
}
Of course that was just an ugly mishmash of a code, but I hope it conveys what
I'm trying to get at:
1. JavaScript will `GET` a URL.
2. Read the source.
3. Interpret source as JSON.
4. Assign it to a variable.
Answer: Newer browser support JSON parsing natively.
You can say `JSON.parse('json data')`. For older browsers (such as IE 7 or 6),
you can use this library: <https://github.com/douglascrockford/JSON-js>
Use `json2.js` from above library. It checks if native browser implementation
is present, if not, adds it.
Do not use `eval` (as [eval is
evil](http://blogs.msdn.com/b/ericlippert/archive/2003/11/01/53329.aspx))!
**Update:** To get the 'json data', use this:
var jsonObject = {};
var xhr = new XMLHttpRequest();
xhr.open( "GET", url, true ); // true makes this call asynchronous
xhr.onreadystatechange = function () { // need eventhandler since our call is async
if ( xhr.readyState == 4 && xhr.status == 200 ) { // check for success
jsonObject = JSON.parse( xhr.responseText );
}
};
xhr.send(null);
Also, I would suggest reading this
[article](http://www.ilinsky.com/articles/XMLHttpRequest/) for cross browser
issues and implementation of `XMLHttpRequest` object.
|
wxPython: Disable a notebook tab?
Question: Is there anyway to disable a notebook tab? Like you can with the Widgets
themselves? I have a long process I kick off, and while it should be pretty
self-explanatory for those looking at it, I want to be able to prevent the
user from mucking around in other tabs until the process it is running is
complete.
I couldn't seem to find anything in `wx.Notebook` to help with this?
Code snippet:
def __init__(self, parent):
wx.Notebook.__init__(self, parent, id=wx.ID_ANY, style=wx.BK_DEFAULT)
self.AddPage(launchTab.LaunchPanel(self), "Launch")
self.AddPage(scanTab.ScanPanel(self), "Scan")
self.AddPage(extractTab.ExtractPanel(self), "Extract")
self.AddPage(virtualsTab.VirtualsPanel(self), "Virtuals")
Answer: It si not doable with `wx.Notebook`. But you can use some of the more advanced
widgets such as `wx.lib.agw.aui.AuiNotebook`:
import wx
import wx.lib.agw.aui as aui
class MainWindow(wx.Frame):
def __init__(self, *args, **kwargs):
wx.Frame.__init__(self, *args, **kwargs)
style = aui.AUI_NB_DEFAULT_STYLE ^ aui.AUI_NB_CLOSE_ON_ACTIVE_TAB
self.notebook = aui.AuiNotebook(self, agwStyle=style)
self.panel1 = wx.Panel(self.notebook)
self.panel2 = wx.Panel(self.notebook)
self.panel3 = wx.Panel(self.notebook)
self.notebook.AddPage(self.panel1, "First")
self.notebook.AddPage(self.panel2, "Second")
self.notebook.AddPage(self.panel3, "Third")
self.notebook.EnableTab(1, False)
self.Show()
app = wx.App(False)
win = MainWindow(None)
app.MainLoop()
|
Accessing an RFID reader via a computer from a server
Question: On a computer I want to run a web-based application which is served by a
server and this application have to access an RFID reader.
I have set this computer to connect to the server via wireless LAN and connect
to the RFID reader via an Ethernet cable (tried both straight through and
crossover cable). The reader cannot connect to the server directly because of
the mobility needed.
Setting up the connection appear in the image below. The server assigned IP
address for the computer using DHCP. Connection between the computer and the
reader have set by static.
Clearly, the computer can access both the server and the reader but the server
cannot access the reader as I needed.
EDIT:
The application is developed using Python with Django framework. To connect to
the reader I just simply used `socket`.
import socket
HOST = '192.168.1.21'
PORT = 50007
soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
soc.settimeout(2)
soc.connect((HOST, PORT))
Answer: I would implement a java-applet and upload it on the server. When user opens a
page from this server, java applet loads and starts working. Applet is running
on the user's computer context and can access RFID reader, and pass this
information to the server.
If accessing RFID-reader requires to involve dll-libraries or any native OS
modules, then this applet has to be signed. Use keytool and jarsigner tools
from Java SDK to sign the applet before uploading it to the server.
[Here you can find information on java
networking](http://download.oracle.com/javase/tutorial/networking/index.html).
[And here you can find information on java applet
technology](http://download.oracle.com/javase/tutorial/deployment/applet/)
|
Given two python lists of same length. How to return the best matches of similar values?
Question: Given are two python lists with strings in them (names of persons):
list_1 = ['J. Payne', 'George Bush', 'Billy Idol', 'M Stuart', 'Luc van den Bergen']
list_2 = ['John Payne', 'George W. Bush', 'Billy Idol', 'M. Stuart', 'Luc Bergen']
I want a mapping of the names, that are most similar.
'J. Payne' -> 'John Payne'
'George Bush' -> 'George W. Bush'
'Billy Idol' -> 'Billy Idol'
'M Stuart' -> 'M. Stuart'
'Luc van den Bergen' -> 'Luc Bergen'
Is there a neat way to do this in python? The lists contain in average 5 or 6
Names. Sometimes more, but this is seldom. Sometimes it is just one name in
every list, which could be spelled slightly different.
Answer: Using the function defined here:
<http://hetland.org/coding/python/levenshtein.py>
>>> for i in list_1:
... print i, '==>', min(list_2, key=lambda j:levenshtein(i,j))
...
J. Payne ==> John Payne
George Bush ==> George W. Bush
Billy Idol ==> Billy Idol
M Stuart ==> M. Stuart
Luc van den Bergen ==> Luc Bergen
You could use functools.partial instead of the lambda
>>> from functools import partial
>>> for i in list_1:
... print i, '==>', min(list_2, key=partial(levenshtein,i))
...
J. Payne ==> John Payne
George Bush ==> George W. Bush
Billy Idol ==> Billy Idol
M Stuart ==> M. Stuart
Luc van den Bergen ==> Luc Bergen
|
Eclipse - interactive shell for python not working
Question: I've installed and configured Pydev with Eclipse but when I try to use
interactive shell I get errors. Can someone have a look and advise?
Code for two functions:
def convert_milage(t): # t - number of miles per 1 gallon
litersPer100Kilometers = 100/ ((t * 1.609) / 3.785)
return litersPer100Kilometers
def liters_needed(t, v): # t: distance in kms, v: fuel consumption
fuelConsumption = convert_milage(v)
litersNeeded = (t * fuelConsumption) / 100
return litersNeeded
Error: <http://i54.tinypic.com/2afmu7p.png>
Error message:
>>> convert_milage(100)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'convert_milage' is not defined
>>>
Answer: You need to open the console for the file you're in, not just use the general
python console, as that knows nothing about the functions in your source file.
Press `Ctrl-Alt-Enter` and select `Current active editor`.
That should import the current module into your shell and make things work
better.
|
Perl Compatible Regular Expression (PCRE) in Python
Question: I have to parse some strings based on PCRE in Python and I've no idea how to
do that.
Strings I want to parse looks like :
match mysql m/^.\0\0\0\n(4\.[-.\w]+)\0...\0/s p/MySQL/ i/$1/
In this example, I have to get this different items :
"m/^.\0\0\0\n(4\.[-.\w]+)\0...\0/s" ; "p/MySQL/" ; "i/$1/"
The only thing I've found relating to PCRE manipulation in Python is this
module : <http://pydoc.org/2.2.3/pcre.html> (but it's written it's a .so ..)
Do you know if some python module exist to parse this kind of string ?
Answer: # Be Especially Careful with non‐ASCII in Python
There are some really subtle issues with how Python deals with, or fails to
deal with, non-ASCII in patterns and strings. Worse, these disparities vary
substantially according not just to which version of Python you are using, but
also whether you have a “wide build”.
In general, when you’re doing Unicode stuff, **Python3 with a wide build works
best** and Python2 with a narrow build works worst, but all combinations are
still a pretty far cry far from how Perl regexes work _vis‐à‐vis_ Unicode. If
you’re looking for ᴘᴄʀᴇ patterns in Python, you may have to look a bit further
afield than its old `re` module.
**EDIT** : The vexing “wide-build” issues have **_finally_ been fixed** once
and for all — provided you use a sufficiently advanced release of Python.
Here’s an excerpt from [the v3.3 release
notes](http://docs.python.org/dev/whatsnew/3.3.html):
> ## _Functionality_
>
> Changes introduced by [PEP 393](http://www.python.org/dev/peps/pep-0393) are
> the following:
>
> * Python now always supports the full range of Unicode codepoints,
> including non-BMP ones (i.e. from U+0000 to U+10FFFF). The distinction
> between narrow and wide builds no longer exists and Python now behaves like
> a wide build, even under Windows.
> * With the death of narrow builds, the problems specific to narrow builds
> have also been fixed, for example:
> * `len()` now always returns 1 for non-BMP characters, so
> `len('\U0010FFFF') == 1`;
> * surrogate pairs are not recombined in string literals, so
> `'\uDBFF\uDFFF' != '\U0010FFFF'`;
> * indexing or slicing non-BMP characters returns the expected value, so
> `'\U0010FFFF'[0]` now returns `'\U0010FFFF'` and not `'\uDBFF'`;
> * all other functions in the standard library now correctly handle non-
> BMP codepoints.
> * The value of `sys.maxunicode` is now always 1114111 (0x10FFFF in
> hexadecimal). The `PyUnicode_GetMax()` function still returns either 0xFFFF
> or 0x10FFFF for backward compatibility, and it should not be used with the
> new Unicode API (see [issue 13054](http://bugs.python.org/issue13054)).
> * `The ./configure` flag `--with-wide-unicode` has been removed.
>
## The Future of Python Regexes
In contrast to what’s currently available in the standard Python
distribution’s `re` library, [Matthew Barnett’s `regex` module for both Python
2 and Python 3 alike](http://pypi.python.org/pypi/regex) is much, much better
in pretty much all possible ways, and will quite probably replace `re`
eventually. Its particular relevance to your question is that his `regex`
library is far more ᴘᴄʀᴇ (_i.e._ **it’s much more Perl‐compatible**) in every
way than `re` now is, which will make porting Perl regexes to Python easier
for you. Because it is a ground‐up rewrite (as in from‐scratch not as in
hamburger :), it was written with non-ASCII in mind, which `re` was not.
The `regex` library therefore much more closely follows the (current)
recommendations of [UTS#18: Unicode Regular
Expressions](http://unicode.org/reports/tr18/) in how it approaches things. It
**meets or exceeds the UTS#18 Level 1 requirements** in most if not all
regards, something you normally have to use the ICU regex library or Perl
itself for — or if you are especially courageous, the new Java 7 update to its
regexes, as that also conforms to the [Level One
requirements](http://unicode.org/reports/tr18/#Basic_Unicode_Support) from
UTS#18.
Beyond meeting those Level One requirements, which are all absolutely
essential for basic Unicode support but which are **not met by Python’s
current`re` library,** the awesome `regex` library also meets the Level Two
requirements for [RL2.5](http://unicode.org/reports/tr18/#Name_Properties)
Named Characters (`\N{...})`),
[RL2.2](http://unicode.org/reports/tr18/#Default_Grapheme_Clusters) Extended
Grapheme Clusters (`\X`), and the new RL2.7 on Full Properties from [revision
14 of UTS#18](http://www.unicode.org/reports/tr18/tr18-14.html).
Matthew’s `regex` module also does Unicode casefolding so that case
insensitive matches work reliabably on Unicode, **which`re` does not.**
**EDIT** : The following is no longer true, because `regex` now supports full
Unicode casefolding, like Perl and Ruby.
> > ~~One super‐tiny difference is that for now, Perl’s case‐insensitive
> patterns use full string‐oriented casefolds while his`regex` module still
> uses simple single‐char‐oriented casefolds, but this is something he’s
> looking into. It’s actually a very hard problem, one which apart from Perl,
> only Ruby even attempts.~~
Under full casefolding, this means that (for example) `"ß"` now correct
matches `"SS"`, `"ss"`, `"ſſ"`, `"ſs"` (etc.) when case-insensitive matching
is selected. (This is admittedly more important in the Greek script than the
Latin one.)
See also the slides or doc source code from [my 3rd OSCON2011
talk](http://training.perl.com/OSCON2011/index.html) entitled _“**Unicode
Support Shootout: The Good, the Bad, and the (mostly) Ugly** ”_ for general
issues in Unicode support across Javascripts, PHP, Go, Ruby, Python, Java, and
Perl. If can’t use either Perl regexes or possibly the ICU regex library
(which doesn’t have named captures, alas!), then Matthew’s `regex` for Python
is probably your best shot.
* * *
Nᴏᴛᴀ Bᴇɴᴇ s.ᴠ.ᴘ. (= _s’il vous plaît, et même s’il ne vous plaît pas_ :) The
following unsolicited noncommercial nonadvertisement was _not_ actually put
here by the author of the Python `regex` library. :)
## Cool `regex` Features
The Python `regex` library has a **cornucopeia of superneat features** , some
of which are found in no other regex system anywhere. These make it very much
worth checking out no matter whether you happen to be using it for its
ᴘᴄʀᴇ‐ness or its stellar Unicode support.
A few of this module’s outstanding features of interest are:
* **Variable‐width lookbehind** , a feature which is quite rare in regex engines and very frustrating not to have when you really want it. This may well be the most frequently requested feature in regexes.
* Backwards searching so you don’t have to reverse your string yourself first.
* Scoped `ismx`‐type options, so that `(?i:foo)` only casefolds for foo, not overall, or `(?-i:foo)` to turn it off just on foo. This is how Perl works (or can).
* Fuzzy matching based on edit‐distance (which Udi Manber’s `agrep` and `glimpse` also have)
* Implicit shortest‐to‐longest sorted named lists via `\L<list>` interpolation
* Metacharacters that specifically match only the start or only the end of a word rather than either side (`\m`, `\M`)
* Support for all Unicode line separators (Java can do this, as can Perl albeit somewhat begrudgingly with `\R` per [RL1.6](http://unicode.org/reports/tr18/#Line_Boundaries).
* Full set operations — union, intersection, difference, and symmetric difference — on bracketed character classes per [RL1.3](http://unicode.org/reports/tr18/#Subtraction_and_Intersection), which is much easier than getting at it in Perl.
* Allows for repeated capture groups like `(\w+\s+)+` where you can get all separate matches of the first group not just its last match. (I believe C♯ might also do this.)
* A more straightfoward way to get at overlapping matches than sneaky capture groups in lookaheads.
* Start and end positions for all groups for later slicing/substring operations, much like Perl’s `@+` and `@-` arrays.
* The branch‐reset operator via `(?|...|...|...|)` to reset group numbering in each branch the way it works in Perl.
* Can be configured to have your coffee waiting for you in the morning.
* Support for the more sophisticated word boundaries from [RL2.3](http://unicode.org/reports/tr18/#Default_Word_Boundaries).
* Assumes Unicode strings by default, and fully supports [RL1.2a](http://unicode.org/reports/tr18/#Compatibility_Properties) so that `\w`, `\b`, `\s`, and such work on Unicode.
* Supports `\X` for graphemes.
* Supports the `\G` continuation point assertion.
* Works correctly for 64‐bit builds (`re` only has 32‐bit indices).
* Supports multithreading.
Ok, that’s enough hype. :)
# Yet Another Fine Alternate Regex Engine
One final alternative that is worth looking at if you are a regex geek is the
[Python library bindings](http://pypi.python.org/pypi/re2/) to Russ Cox’s
awesome [RE2 library](http://swtch.com/~rsc/regexp/). It also supports Unicode
natively, including simple char‐based casefolding, and unlike `re` it notably
provides for both the Unicode General Category and the Unicode Script
character properties, which are the two key properties you most often need for
the simpler kinds of Unicode processing.
Although RE2 misses out on a few Unicode features like `\N{...}` named
character support found in ICU, Perl, and Python, it has extremely serious
computational advantages that make it **the regex engine of choice** whenever
you’re concern with starvation‐based denial‐of‐service attacks through regexes
in web queries and such. It manages this by forbidding backreferences, which
cause a regex to stop being regular and risk super‐exponential explosions in
time and space.
Library bindings for RE2 are available not just for C/C++ and Python, but also
for Perl and most especially for Go, where it is slated to very shortly
replace the standard regex library there.
|
cannot urlencode() after storing QueryDict in session
Question: I tried to post this to django-users group (
<http://groups.google.com/group/django-
users/browse_thread/thread/8572d7f4075cfe0e> ) but got no responses. Maybe
here I will get more help.
I store `request.GET` in session:
request.session['query_string'] = request.GET
then I retrieve the value in another page and try to urlencode the QueryDict:
context['query_string'] = request.session['query_string'].urlencode()
in my context I get the python's string representation of the QueryDict object
instead of the expected `key0=value0&key1=value1&...` string.
If, instead of QueryDict, I store the urlencoded string in the session,
everything works of course:
request.session['query_string'] = request.GET.urlencode()
is it a bug?
Answer: This is not a bug. If you take a peek at the `QueryDict` definition (see
[https://github.com/django/django/blob/master/django/http/**init**.py](https://github.com/django/django/blob/master/django/http/__init__.py)),
it says explicitly that it's immutable unless you create a copy of it.
To demonstrate this, here's what I have in my Python shell,
>>> from django.http import QueryDict
>>> q1 = QueryDict('', mutable=False)
>>> q2 = QueryDict('', mutable=True)
>>> q1['next'] = '/a&b/'
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/Users/kenny/Desktop/Kreybits/locker/python/lib/python2.7/site-packages/django/http/__init__.py", line 357, in __setitem__
self._assert_mutable()
File "/Users/kenny/Desktop/Kreybits/locker/python/lib/python2.7/site-packages/django/http/__init__.py", line 354, in _assert_mutable
raise AttributeError("This QueryDict instance is immutable")
AttributeError: This QueryDict instance is immutable
>>> q2['next'] = '/a&b/'
>>> q2.urlencode()
'next=%2Fa%26b%2F'
The `mutable` argument is set to False by default, and since
`request.session['query_string'] = request.GET` initialized it to an empty
QueryDict to begin with, calling `urlencode()` only returns you an empty str
while the `request.session['query_string'] = request.GET.urlencode()` works
because you're working with a QueryDict that has been initialized with the
appropriate key/values.
|
webapp2 + jinja2: How can i get uri_for() working in jinja2-views
Question: How can i add pass Model-Specific urls to the Template. Let's say, i want to
build an edit-link. I would guess, using the uri_for() function would be an
easy approach.
But the following gives me "UndefinedError: 'webapp2' is undefined"
{% webapp2.uri_for("editGreeting", greeting.key().id()) %}
Or should i prepare these in the MainPage-Request-Handler? If so, i don't know
how to add them to each greeting.
The following Code-Example is taken from: <http://webapp-
improved.appspot.com/tutorials/gettingstarted/templates.html>
Controller/Handler
class MainPage(webapp2.RequestHandler):
def get(self):
guestbook_name=self.request.get('guestbook_name')
greetings_query = Greeting.all().ancestor(
guestbook_key(guestbook_name)).order('-date')
greetings = greetings_query.fetch(10)
if users.get_current_user():
url = users.create_logout_url(self.request.uri)
url_linktext = 'Logout'
else:
url = users.create_login_url(self.request.uri)
url_linktext = 'Login'
template_values = {
'greetings': greetings,
'url': url,
'url_linktext': url_linktext,
}
path = os.path.join(os.path.dirname(__file__), 'index.html')
self.response.out.write(template.render(path, template_values))
Template/View:
<html>
<body>
{% for greeting in greetings %}
{% if greeting.author %}
<b>{{ greeting.author.nickname }}</b> wrote:
{% else %}
An anonymous person wrote:
{% endif %}
<blockquote>{{ greeting.content|escape }}</blockquote>
{% endfor %}
<form action="/sign" method="post">
<div><textarea name="content" rows="3" cols="60"></textarea></div>
<div><input type="submit" value="Sign Guestbook"></div>
</form>
<a href="{{ url }}">{{ url_linktext }}</a>
</body>
</html
The class BaseHandler is the class all handlers inherit from. I tried the
following as @moraes suggested. I still get:
value = self.func(obj)
File "C:\Users\timme04\python\hellowebapp\handlers\basehandler.py", line 23, in jinja2
return jinja2.get_jinja2(factory=self.jinja2_factory)
File "C:\Users\timme04\python\hellowebapp\webapp2_extras\jinja2.py", line 212, in get_jinja2
jinja2 = app.registry[key] = factory(app)
TypeError: jinja2_factory() takes exactly 1 argument (2 given)
:(
import webapp2
from webapp2_extras import jinja2
class BaseHandler(webapp2.RequestHandler):
def jinja2_factory(app):
j = jinja2.Jinja2(app)
j.environment.filters.update({
# Set filters.
# ...
})
j.environment.globals.update({
# Set global variables.
'uri_for': webapp2.uri_for,
# ...
})
return j
@webapp2.cached_property
def jinja2(self):
# Returns a Jinja2 renderer cached in the app registry.
return jinja2.get_jinja2(factory=self.jinja2_factory)
def render_response(self, _template, **context):
# Renders a template and writes the result to the response.
rv = self.jinja2.render_template(_template, **context)
self.response.write(rv)
Answer: You must set `uri_for` as a global variable. One way to do it is to set an
initializer for global variables and filters:
import webapp2
from webapp2_extras import jinja2
def jinja2_factory(app):
j = jinja2.Jinja2(app)
j.environment.filters.update({
# Set filters.
# ...
})
j.environment.globals.update({
# Set global variables.
'uri_for': webapp2.uri_for,
# ...
})
return j
class BaseHandler(webapp2.RequestHandler):
@webapp2.cached_property
def jinja2(self):
# Returns a Jinja2 renderer cached in the app registry.
return jinja2.get_jinja2(factory=jinja2_factory)
def render_response(self, _template, **context):
# Renders a template and writes the result to the response.
rv = self.jinja2.render_template(_template, **context)
self.response.write(rv)
Edit: changed example to use a RequestHandler.
|
rpy2 plot problem
Question: I use rpy2-2.0.8, R-2.11.1, Python-2.6.2 on Windows XP.
When I run this script, output image is filled with text message. I suppose
this message is function definition of clusplot.
[test.py]
#!/usr/bin/env python
# -*- mode: python -*- -*- coding: utf-8 -*-
import rpy2.robjects as ro
r = ro.r
# read from csv file
dataf = r('read.csv("test.csv", header=T, row.names="name")')
# k-means
r.library('cluster')
k = 2
cluster = r.kmeans(r.cmdscale(r.dist(dataf)), k)
# plot
r.jpeg('output.jpg')
r.clusplot(r.pam(dataf, k))
r('dev.off()')
[test.csv]
name,a,b,c,d,e,f,g,e,h,I,j,k
x1,1421,99.4,19.5,241.4,103.7,18.8,13.4,4.8,76.3,535.6,28.6,10.3
x2,1495,97.8,22.5,263.3,160.3,9.1,13.7,4.3,93.8,568,33.3,10.4
x3,2649,95.8,14.6,198.6,94.6,15.9,11.6,11.7,85,521.5,52.7,8.71
x4,3251,100.2,27.5,240.9,121,28,13.3,18.9,99.1,336.1,5.1,3.03
x5,2705,100.3,15.3,157.1,95.3,23.4,7.5,17,87.9,366.8,12.1,3.59
x6,3157,100.3,12.4,164,97.1,10.2,8.8,17.4,98.4,418.5,24.2,4.45
x7,2045,104.4,25.3,246.3,131,16.6,14,19.1,96.9,584.2,7.8,6.73
x8,2228,99.1,21.7,246.9,112.2,23.3,15.1,5.3,88.4,415.5,54.2,4.03
x9,2037,100.1,30,296.6,150.7,31.5,15.4,17.8,93.1,346.8,6.1,3.47
x10,2336,99.7,17.6,210.8,116.5,21.5,12.6,10.1,69.9,411,63.9,16.5
x11,1264,101.8,29.3,256.1,126.2,14.3,14.8,5.4,94,540.1,28.5,7.46
x12,1566,98.8,23.7,285.3,128.6,15.1,15.5,8.5,91.5,549.3,59.2,10.5
x13,2210,98.8,28.3,234.4,143.2,17.3,12.7,11.2,95.6,492.1,53.5,8.6
But I use R console (not rpy2), No text overwapping problem.
Does anyone help me?
Answer: I have solved this problem by myself.
R plot command completes the plot title automatically when it is not given. R
command with console and via rpy2 have different behavior for this complement.
(I think it is a kind of bug for rpy2)
So set the title with "main" argument explicitly like this.
# plot
r.jpeg('output.jpg')
r.clusplot(r.pam(dataf, k), main="result")
r('dev.off()')
|
How do closures work in runpy?
Question: I get unexpected behaviour when I try to run methods defined in a file loaded
using the [runpy](http://docs.python.org/library/runpy.html) module. The
methods do not see any variables (including imported modules) defined outside
of that method. Here is how I am doing it:
#test.py
import runpy
env = runpy.run_path('test', {'y':'world'})
env['fn']()
~
#test
import re
print(re.compile(r'^hello', re.IGNORECASE).sub('', "hello world"))
x = "hello"
print(x)
print(y)
def fn():
try:
print(re.compile(r'^hello', re.IGNORECASE).sub('', "hello world"))
except:
print("No re")
try:
print(x)
except:
print("No x")
try:
print(y)
except:
print("No y")
My expected output of test.py would be:
world
hello
world
world
hello
world
because fn would form a closure for re, x and y.
However, instead I get:
world
hello
world
No re
None
None
It looks like re isn't defined within fn even though it should be with normal
closure behaviour. x and y are even stranger because they appear to be defined
but set to None.
Why is this and how do closures work with runpy? How can I achieve normal
behaviour such that fn can 'see' outside variables?
Answer: OK, this is a curiosity of the way Python handles modules, which I know about
but don't fully understand. I've come across it while working on IPython,
where it's explained in [a
comment](https://github.com/ipython/ipython/blob/master/IPython/core/interactiveshell.py#L894).
When Python runs a module, it produces a module object, the attributes of
which are the global names in the module. When the module falls out of scope
and is being destroyed, these attributes are set to `None`. Code which was
defined in the function then sees these as the globals, as you found. You can
demonstrate this by adding `def g(): return globals()` to your file, then
calling `env["g"]()`.
I don't know if there's a way round this with `runpy`. IPython uses some
complicated code to reuse a module object for running other files, caching
copies of its `__dict__` to keep the references therein alive. Have a look at
the [`magic_run`
function](https://github.com/ipython/ipython/blob/master/IPython/core/magic.py#L1445)
if you're interested.
|
django-haystack problem when saving query in session
Question: I want to save the user input in my view, I don't know how to do it redefining
the searchview so I did this:
request.session['q']=request.GET.get('q')
from haystack.views import SearchView
search_view = SearchView(template = template_name)
return search_view(request)
but I got this error:
Traceback (most recent call last):
File "/home/usu/mysites/gondor/local/lib/python2.7/site-packages/django/core/servers/basehttp.py", line 280, in run
self.result = application(self.environ, self.start_response)
File "/home/usu/mysites/gondor/local/lib/python2.7/site-packages/django/core/servers/basehttp.py", line 674, in __call__
return self.application(environ, start_response)
File "/home/usu/mysites/gondor/local/lib/python2.7/site-packages/django/core/handlers/wsgi.py", line 245, in __call__
response = middleware_method(request, response)
File "/home/usu/mysites/gondor/local/lib/python2.7/site-packages/django/contrib/sessions/middleware.py", line 36, in process_response
request.session.save()
File "/home/usu/mysites/gondor/local/lib/python2.7/site-packages/django/contrib/sessions/backends/db.py", line 57, in save
session_data = self.encode(self._get_session(no_load=must_create)),
File "/home/usu/mysites/gondor/local/lib/python2.7/site-packages/django/contrib/sessions/backends/base.py", line 88, in encode
pickled = pickle.dumps(session_dict, pickle.HIGHEST_PROTOCOL)
File "/usr/local/lib/python2.7/dist-packages/haystack/models.py", line 175, in __getstate__ del(ret_dict['searchsite'])
KeyError: 'searchsite'
If I remove the line:
request.session['q']=request.GET.get('q')
the search works ok, I don't know if there is a problem with haystack or I'm
doing something wrong. Thanks.
Answer: Finally I found the problem. In another view I was saving in the session the
result of a SerchQuerySet, but the problem didn't raised at the time I've put
the content but it raised when I've put other thing in the session. This was
very difficult to find out.
|
Add django model manager code-completion to Komodo
Question: I have been using ActiveState Komodo for a while and while most of the code-
completion is spot on it lacks the code completion from Django's model
manager.
I have included the Django directory in my `PYTHONPATH` and get most of the
code completion, the notable exception being the models.
Assuming I have a model `users` I would expect the code `users.objects.` to
show autocomplete options such as `all()`,`count()`,`filter()` etc. however
these are added by the model's manager which does so in a seemingly abnormal
way.
I am wondering if I can 'force' Komodo to pick up the models.
The model manager looks to be included from the following code (taken from
manager.py)
def ensure_default_manager(sender, **kwargs):
"""
Ensures that a Model subclass contains a default manager and sets the
_default_manager attribute on the class. Also sets up the _base_manager
points to a plain Manager instance (which could be the same as
_default_manager if it's not a subclass of Manager).
"""
cls = sender
if cls._meta.abstract:
return
if not getattr(cls, '_default_manager', None):
# Create the default manager, if needed.
try:
cls._meta.get_field('objects')
raise ValueError("Model %s must specify a custom Manager, because it has a field named 'objects'" % cls.__name__)
except FieldDoesNotExist:
pass
cls.add_to_class('objects', Manager())
cls._base_manager = cls.objects
...
Specifically the last two lines. Is there any way to tell Komodo that
`<model>.objects = Manager()` so the proper code completion is shown?
Answer: Probably the easiest way to get this to work seems to be to add the following
to the top of models.py:
from django.db.models import manager
and then under each model add
objects = manager.Manager()
so that, for example, the following:
class Site(models.Model):
name = models.CharField(max_length=200)
prefix = models.CharField(max_length=1)
secret = models.CharField(max_length=255)
def __unicode__(self):
return self.name
becomes
class Site(models.Model):
name = models.CharField(max_length=200)
prefix = models.CharField(max_length=1)
secret = models.CharField(max_length=255)
objects = manager.Manager()
def __unicode__(self):
return self.name
This is how you would (explicitly) set your own model manager, and by
explicitly setting the model manager (to the default) Kommodo picks up the
code completion perfectly.
Hopefully this will help someone :-)
|
Using PIL to fill empty image space with nearby colors (aka inpainting)
Question: I create an image with PIL:
I need to fill in the empty space (depicted as black). I could easily fill it
with a static color, but what I'd like to do is fill the pixels in with nearby
colors. For example, the first pixel after the border might be a Gaussian blur
of the filled-in pixels. Or perhaps a push-pull type algorithm described in
[The Lumigraph, Gortler, et
al.](http://research.microsoft.com/apps/pubs/default.aspx?id=68168).
I need something that is not too slow because I have to run this on many
images. I have access to other libraries, like numpy, and you can assume that
I know the borders or a mask of the outside region or inside region. Any
suggestions on how to approach this?
**UPDATE:**
As suggested by belisarius, [opencv's
inpaint](http://opencv.willowgarage.com/documentation/cpp/miscellaneous_image_transformations.html#cv-
inpaint) method is perfect for this. Here's some python code that uses opencv
to achieve what I wanted:
import Image, ImageDraw, cv
im = Image.open("u7XVL.png")
pix = im.load()
#create a mask of the background colors
# this is slow, but easy for example purposes
mask = Image.new('L', im.size)
maskdraw = ImageDraw.Draw(mask)
for x in range(im.size[0]):
for y in range(im.size[1]):
if pix[(x,y)] == (0,0,0):
maskdraw.point((x,y), 255)
#convert image and mask to opencv format
cv_im = cv.CreateImageHeader(im.size, cv.IPL_DEPTH_8U, 3)
cv.SetData(cv_im, im.tostring())
cv_mask = cv.CreateImageHeader(mask.size, cv.IPL_DEPTH_8U, 1)
cv.SetData(cv_mask, mask.tostring())
#do the inpainting
cv_painted_im = cv.CloneImage(cv_im)
cv.Inpaint(cv_im, cv_mask, cv_painted_im, 3, cv.CV_INPAINT_NS)
#convert back to PIL
painted_im = Image.fromstring("RGB", cv.GetSize(cv_painted_im), cv_painted_im.tostring())
painted_im.show()
And the resulting image:
Answer: A method with nice results is the [**Navier-Stokes Image
Restoration**.](http://www.dtic.upf.edu/~mbertalmio/final-cvpr.pdf) I know
OpenCV has it, don't know about PIL.
Your example:
 
I did it with Mathematica.
**Edit**
As per your reuquest, the code is:
i = Import["http://i.stack.imgur.com/uEPqc.png"];
Inpaint[i, ColorNegate@Binarize@i, Method -> "NavierStokes"]
The ColorNegate@ ... part creates the replacement mask. The filling is done
with just the `Inpaint[]` command.
|
Repeatedly extract a line between two delimiters in a text file, Python
Question: I have a text file in the following format:
DELIMITER1
extract me
extract me
extract me
DELIMITER2
I'd like to extract every block of `extract me`s between DELIMITER1 and
DELIMITER2 in the .txt file
This is my current, non-performing code:
import re
def GetTheSentences(file):
fileContents = open(file)
start_rx = re.compile('DELIMITER')
end_rx = re.compile('DELIMITER2')
line_iterator = iter(fileContents)
start = False
for line in line_iterator:
if re.findall(start_rx, line):
start = True
break
while start:
next_line = next(line_iterator)
if re.findall(end_rx, next_line):
break
print next_line
continue
line_iterator.next()
Any ideas?
Answer: You can simplify this to one regular expression using `re.S`, the [DOTALL
flag](http://docs.python.org/library/re.html#re.DOTALL).
import re
def GetTheSentences(infile):
with open(infile) as fp:
for result in re.findall('DELIMITER1(.*?)DELIMITER2', fp.read(), re.S):
print result
# extract me
# extract me
# extract me
This also makes use of the non-greedy operator `.*?`, so multiple non-
overlapping blocks of DELIMITER1-DELIMITER2 pairs will all be found.
|
Create PDF with (resized) PNG images using Pycairo - rescaling Surface issue
Question: I have som PNG image links that I want to download, "convert to thumbnails"
and save to PDF using Python and Cairo.
Now, I have a working code, but I don't know how to control image size on
paper. Is there a way to resize a PyCairo Surface to the dimensions I want
(which happens to be smaller than the original)? I want the original pixels to
be "shrinked" to a higher resolution (on paper).
Also, I tried `Image.rescale()` function from PIL, but it gives me back a
20x20 pixel output (out of a 200x200 pixel original image, which is not the
banner example on the code). What I want is a 200x200 pixel image plotted
inside a 20x20 mm square on paper (instead of a 200x200 mm square as I am
getting now)
My current code is:
#!/usr/bin/python
import cairo, urllib, StringIO, Image # could I do it without Image module?
paper_width = 210
paper_height = 297
margin = 20
point_to_milimeter = 72/25.4
pdfname = "out.pdf"
pdf = cairo.PDFSurface(pdfname , paper_width*point_to_milimeter, paper_height*point_to_milimeter)
cr = cairo.Context(pdf)
cr.scale(point_to_milimeter, point_to_milimeter)
f=urllib.urlopen("http://cairographics.org/cairo-banner.png")
i=StringIO.StringIO(f.read())
im=Image.open(i)
# are these StringIO operations really necessary?
imagebuffer = StringIO.StringIO()
im.save(imagebuffer, format="PNG")
imagebuffer.seek(0)
imagesurface = cairo.ImageSurface.create_from_png(imagebuffer)
### EDIT: best answer from Jeremy, and an alternate answer from mine:
best_answer = True # put false to use my own alternate answer
if best_answer:
cr.save()
cr.scale(0.5, 0.5)
cr.set_source_surface(imagesurface, margin, margin)
cr.paint()
cr.restore()
else:
cr.set_source_surface(imagesurface, margin, margin)
pattern = cr.get_source()
scalematrix = cairo.Matrix() # this can also be used to shear, rotate, etc.
scalematrix.scale(2,2) # matrix numbers seem to be the opposite - the greater the number, the smaller the source
scalematrix.translate(-margin,-margin) # this is necessary, don't ask me why - negative values!!
pattern.set_matrix(scalematrix)
cr.paint()
pdf.show_page()
Note that the beautiful Cairo banner does not even fit the page... The ideal
result would be that I could control the width and height of this image in
user space units (milimeters, in this case), to create a nice header image,
for example.
Thanks for reading and for any help or comment!!
Answer: Try scaling the context when you draw the image.
E.g.
cr.save() # push a new context onto the stack
cr.scale(0.5, 0.5) # scale the context by (x, y)
cr.set_source_surface(imagesurface, margin, margin)
cr.paint()
cr.restore() # pop the context
See: <http://cairographics.org/documentation/pycairo/2/reference/context.html>
for more details.
|
PyQt4: Interrupt QThread exec when GUI is closed
Question: I have a PyQt4 GUI that has three threads. One thread is a data source, it
provides numpy arrays of data. The next thread is a calculation thread, it
takes the numpy array (or multiple numpy arrays) via a Python `Queue.Queue`
and calculates what will be displayed on the GUI. The calculator then signals
the GUI thread (the main thread) via a custom signal and this tells the GUI to
update the matplotlib figure that's displayed.
I'm using the "proper" method described
[here](http://labs.qt.nokia.com/2010/06/17/youre-doing-it-wrong/) and
[here](http://labs.qt.nokia.com/2006/12/04/threading-without-the-headache/).
So here's the general layout. I tried to shorten my typing time and used
comments instead of the actual code in some parts:
class Source(QtCore.QObject):
signal_finished = pyQtSignal(...)
def __init__(self, window):
self._exiting = False
self._window = window
def do_stuff(self):
# Start complicated data generator
for data in generator:
if not self._exiting:
# Get data from generator
# Do stuff - add data to Queue
# Loop ends when generator ends
else:
break
# Close complicated data generator
def prepare_exit(self):
self._exiting = True
class Calculator(QtCore.QObject):
signal_finished = pyQtSignal(...)
def __init__(self, window):
self._exiting = False
self._window = window
def do_stuff(self):
while not self._exiting:
# Get stuff from Queue (with timeout)
# Calculate stuff
# Emit signal to GUI
self._window.signal_for_updating.emit(...)
def prepare_exit(self):
self._exiting = True
class GUI(QtCore.QMainWindow):
signal_for_updating = pyQtSignal(...)
signal_closing = pyQtSignal(...)
def __init__(self):
self.signal_for_updating.connect(self.update_handler, type=QtCore.Qt.BlockingQueuedConnection)
# Other normal GUI stuff
def update_handler(self, ...):
# Update GUI
def closeEvent(self, ce):
self.fileQuit()
def fileQuit(self): # Used by a menu I have File->Quit
self.signal_closing.emit() # Is there a builtin signal for this
if __name__ == '__main__':
app = QtCore.QApplication([])
gui = GUI()
gui.show()
source_thread = QtCore.QThread() # This assumes that run() defaults to calling exec_()
source = Source(window)
source.moveToThread(source_thread)
calc_thread = QtCore.QThread()
calc = Calculator(window)
calc.moveToThread(calc_thread)
gui.signal_closing.connect(source.prepare_exit)
gui.signal_closing.connect(calc.prepare_exit)
source_thread.started.connect(source.do_stuff)
calc_thread.started.connect(calc.do_stuff)
source.signal_finished.connect(source_thread.quit)
calc.signal_finished.connect(calc_thread.quit)
source_thread.start()
calc_thread.start()
app.exec_()
source_thread.wait() # Should I do this?
calc_thread.wait() # Should I do this?
...So, my problems all occur when I try to close the GUI before the sources
are complete, when I let the data generators finish it closes fine:
* While waiting for the threads, the program hangs. As far as I can tell this is because the closing signal's connected slots never get run by the other thread's event loops (they're stuck on the "infinitely" running do_stuff method).
* When the calc thread emits the updating gui signal (a BlockedQueuedConnection signal) right after the GUI closing, it seems to hang. I'm guessing this is because the GUI is already closed and isn't there to accept the emitted signal (judging by the print messages I put in my actual code).
I've been looking through tons of tutorials and documentation and I just feel
like I'm doing something stupid. Is this possible, to have an event loop and
an "infinite" running loop that end early...and safely (resources closed
properly)?
I'm also curious about my BlockedQueuedConnection problem (if my description
makes sense), however this problem is probably fixable with a simple redesign
that I'm not seeing.
Thanks for any help, let me know what doesn't make sense. If it's needed I can
also add more to the code instead of just doing comments (I was kind of hoping
that I did something dumb and it wouldn't be needed).
**Edit:** I found some what of a work around, however, I think I'm just lucky
that it works every time so far. If I make the prepare_exit and the
thread.quit connections DirectConnections, it runs the function calls in the
main thread and the program does not hang.
I also figured I should summarize some questions:
1. **Can a QThread have an event loop (via exec_) and have a long running loop?**
2. **Does a BlockingQueuedConnection emitter hang if the receiver disconnects the slot (after the signal was emitted, but before it was acknowledged)?**
3. **Should I wait for the QThreads (via thread.wait()) after app.exec_(), is this needed?**
4. **Is there a Qt provided signal for when QMainWindow closes, or is there one from the QApplication?**
**Edit 2/Update on progress:** I have created a runnable example of the
problem by adapting [this
post](http://stackoverflow.com/questions/6783194/background-thread-with-
qthread-in-pyqt/6789205#6789205) to my needs.
from PyQt4 import QtCore
import time
import sys
class intObject(QtCore.QObject):
finished = QtCore.pyqtSignal()
interrupt_signal = QtCore.pyqtSignal()
def __init__(self):
QtCore.QObject.__init__(self)
print "__init__ of interrupt Thread: %d" % QtCore.QThread.currentThreadId()
QtCore.QTimer.singleShot(4000, self.send_interrupt)
def send_interrupt(self):
print "send_interrupt Thread: %d" % QtCore.QThread.currentThreadId()
self.interrupt_signal.emit()
self.finished.emit()
class SomeObject(QtCore.QObject):
finished = QtCore.pyqtSignal()
def __init__(self):
QtCore.QObject.__init__(self)
print "__init__ of obj Thread: %d" % QtCore.QThread.currentThreadId()
self._exiting = False
def interrupt(self):
print "Running interrupt"
print "interrupt Thread: %d" % QtCore.QThread.currentThreadId()
self._exiting = True
def longRunning(self):
print "longRunning Thread: %d" % QtCore.QThread.currentThreadId()
print "Running longRunning"
count = 0
while count < 5 and not self._exiting:
time.sleep(2)
print "Increasing"
count += 1
if self._exiting:
print "The interrupt ran before longRunning was done"
self.finished.emit()
class MyThread(QtCore.QThread):
def run(self):
self.exec_()
def usingMoveToThread():
app = QtCore.QCoreApplication([])
print "Main Thread: %d" % QtCore.QThread.currentThreadId()
# Simulates user closing the QMainWindow
intobjThread = MyThread()
intobj = intObject()
intobj.moveToThread(intobjThread)
# Simulates a data source thread
objThread = MyThread()
obj = SomeObject()
obj.moveToThread(objThread)
obj.finished.connect(objThread.quit)
intobj.finished.connect(intobjThread.quit)
objThread.started.connect(obj.longRunning)
objThread.finished.connect(app.exit)
#intobj.interrupt_signal.connect(obj.interrupt, type=QtCore.Qt.DirectConnection)
intobj.interrupt_signal.connect(obj.interrupt, type=QtCore.Qt.QueuedConnection)
objThread.start()
intobjThread.start()
sys.exit(app.exec_())
if __name__ == "__main__":
usingMoveToThread()
You can see by running this code and swapping between the two connection types
on interrupt_signal that the direct connection works because its running in a
separate thread, **proper or bad practice?** I feel like that is bad practice
because I am quickly changing something that another thread is reading. The
QueuedConnection does not work because the event loop must wait until
longRunning is finished before the event loop gets back around to the
interrupt signal, which is not what I want.
**Edit 3:** I remembered reading that `QtCore.QCoreApplication.processEvents`
can be used in cases with long running calculations, but everything I read
said don't use it unless you know what you are doing. Well here is what I
think it's doing (in a sense) and using it seems to work: When you call
processEvents it causes the caller's event loop to hault its current operation
and continue on processing the pending events in the event loop, eventually
continuing the long calculation event. Other recommendations like in [this
email](http://www.mail-archive.com/pyqt@riverbankcomputing.com/msg17349.html)
suggest timers or putting the work in other threads, I think this just makes
my job even more complicated, especially since I've proven(I think) timers
don't work in my case. If processEvents seems to fix all my problems I will
answer my own question later.
Answer: After looking through the mailing list archives, google searching, stack
overflow searching, and thinking about what my question really was and what
the purpose of the question was I came up with this answer:
The short answer being use processEvents(). The long answer is that all my
searching results in people saying "be very careful using processEvents()" and
"avoid it at all costs". I think it should be avoided if you are using it
because you are not seeing results in your GUI main thread fast enough.
Instead of using processEvents in this case, the work being done in the main
thread that is not UI purposed should be moved to another thread (as my design
has done).
The reason my specific problem needs processEvents() is that I want my
QThreads to have two way communication with the GUI thread, which means that
my QThreads have to have an event loop (exec_()) to accept signals from the
GUI. This two way communication is what I meant earlier by "the purpose of the
question". Since my QThreads are meant to run "concurrently" with the main GUI
thread AND because they need to update the GUI and be "updated" by the GUI
(the exit/closing signal in my first example), they need processEvents(). I
think this is what processEvents() is for.
My understanding of processEvents(), as decribed above, is that when called in
a QThread it will block/pause the current event (my longRunning method) while
it continues on through the events in the event loop (only for the QThread
processEvents() was called in). After going through the pending events, the
event loop wraps back around and continues running the event that it paused
(my longRunning method).
I know I didn't answer all my questions, but the main one is answered.
**PLEASE CORRECT ME IF I AM WRONG IN ANY WAY**
**Edit:** Please read Ed's answer and the comments.
|
PYTHON: How to take a .txt file as input from user using raw_input in Python and then read that file row wise?
Question: I want to take a .txt file as input from user through `raw_input`.
Once the input is taken, I want the txt file name given by user to be accessed
and the contents from it written into another file (each in next row).
I am having a problem with how to connect a and b above or how to link raw
input with reading of file. I need help...the code is as follows (but it is
erroneous :S).
import sys,os,csv
x = raw_input("Enter name of file to be written row wise:")
ui = "x" + txt
for ui in x:
data = open("ui").readlines()
outfile = open("myfile.csv","w")
out = csv.writer(outfile)
for row in data:
row = row.strip().split(';')
if row:
for subrow in row:
subrow = subrow.strip().split()
if subrow:
out.writerow(subrow)
outfile.close()
I get the error:
> cannot concatenate 'str' and 'list' objects
Answer:
for row in data:
row = row.strip().split(';')
The fact that you perform `split(';')` has for consequence that a row (you
should write: line) split according to ';' gives always a not empty list, even
if it is an empty line, and even after having been stripped with **strip()** :
`''.split(';')` gives `['']` . So your following condition `if row:` is
useless.
That means that your code is equivalent to:
for row in data:
row = row.strip().split(';')
for subrow in row:
subrow = subrow.split()
if subrow:
out.writerow(subrow)
and then to:
for row in data:
for subrow in row.strip().split(';'):
subrow = subrow.split()
if subrow:
out.writerow(subrow)
.
Moreover , the fact that you use **split()** on **subrow** present in the list
**row.strip().split(';')** eliminates all the blanks before and after each of
the words present in **subrow**. So the first `strip()` in
`row.strip().split(';')` is useless too.
Your code is then equivalent to:
for row in data:
for subrow in row.split(';'):
subrow = subrow.split()
if subrow:
out.writerow(subrow)
Now , `subrow.split()` can produce a void list when subrow is only blanks,
because `split()` without argument has its special algorithm. So the
instruction `if subrow` is usefull.
.
In fact, what your code does is, after having read the content of such a file:
Blackcurrant, Redcurrant ; Orange ; Blueberry
Pear;Chestnut; Lemon Lime, Grapefruit
Apple;Apricot ; Pineapple, Fig; Mulberry, Hedge Apple
to record another file like that:
Blackcurrant
Redcurrant
Orange
Blueberry
Pear
Chestnut
Lemon Lime
Grapefruit
Apple
Apricot
Pineapple
Fig
Mulberry
Hedge
Apple
I prefer the following code to do that:
filename = raw_input("Enter name of file to be written row wise:") + '.txt'
filepath = 'I:\\' + filename
with open(filepath) as handler,open("myfile.csv","wb") as outfile:
out = csv.writer(outfile)
for row in handler:
gen = ( subrow.split() for subrow in row.split(';') )
out.writerow([x for x in gen if x])
del out
.
This code will always run, even for files extremely huge whose content can't
be held by the memory, because the lines of the file are read one after the
other.
In case the file isn't enormous like that, it is possible to proceed like you
did, with **readlines()** :
with open(filepath) as handler:
data = handler.readlines()
with open("myfile.csv","wb") as outfile:
out = csv.writer(outfile)
for row in data:
gen = ( subrow.split() for subrow in row.split(';') )
out.writerow([x for x in gen if x])
del out
But there is no particular interest to proceed so, you can do `for row in
handler` as well.
.
Personnaly, I think it would be better to use writerows():
filename = raw_input("Enter name of file to be written row wise:") + '.txt'
filepath = 'I:\\' + filename
with open(filepath) as handler,open("myfile.csv","wb") as outfile:
out = csv.writer(outfile)
gen = ( x for row in handler for x in (subrow.split() for subrow in row.split(';')) )
out.writerows([x for x in gen if])
del out
.
I end this answer by informing you that a code employing a regex would be far
more efficient:
import csv, re
regx = re.compile('[ ;\r\n]+')
filename = raw_input("Enter name of file to be written row wise:") + '.txt'
filepath = 'I:\\' + filename
with open(filepath) as handler,open("myfile.txt","w") as outfile:
outfile.write('\n'.join(x for x in regx.split(handler.read()) if x))
## Edit 1
handler = open(filepath)
outfile = open("myfile.txt","wb")
out = csv.writer(outfile)
for row in handler:
gen = ( subrow.split() for subrow in row.split(';') )
out.writerow([x for x in gen if x])
del out
outfile.close()
handler.close()
or
import csv, re
regx = re.compile('[ ;\r\n]+')
filename = raw_input("Enter name of file to be written row wise:") + '.txt'
filepath = 'I:\\' + filename
handler = open(filepath)
outfile = open("myfile.txt","w")
outfile.write('\n'.join(x for x in regx.split(handler.read()) if x))
outfile.close()
handler.close()
|
Windows - running .py directly vs running python blah.py behaves differently
Question: I have a python script that uses subprocess:
import subprocess
print "Running stuff"
subprocess.check_call(["do_stuff.bat"])
print "Stuff run"
If this was named blah.py, and I run (from a command prompt):
python blah.py
I will get the output from do_stuff.bat (or whatever I run).
If this is run as:
blah.py
Then I do not get output from do_stuff.bat, only the print statements.
So far seen on windows Server 2003. Python version 2.5.2 (stuck there for
various reasons). Looking at the associated file type action I see:
Python.File="C:\Python25\python.exe" "%1" %*
So can anyone explain the difference?
Answer: I had common problem using threads, but all of my code was in python. Threads
can not write to standard output using print. Just main thread could do that.
I used somethnig like this
import sys
sys.stdout.write("this was printed by thread")
I know that probably it wont help you with bat file...
|
Easy_install and Pip doesn't work
Question: Easy_install and Pip doesn't work anymore on python 2.7, when I try to do:
sudo easy_install pip
I get:
Traceback (most recent call last):
File "/usr/bin/easy_install", line 5, in <module>
from pkg_resources import load_entry_point
File "/usr/bin/lib/python2.7/site-packages/distribute-0.6.19-py2.7.egg/pkg_resources.py", line 2713, in <module>
parse_requirements(__requires__), Environment()
File "/usr/bin/lib/python2.7/site-packages/distribute-0.6.19-py2.7.egg/pkg_resources.py", line 584, in resolve
raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: distribute==0.6.15
And when I try:
sudo pip install [package]
I get:
Traceback (most recent call last):
File "/usr/bin/pip", line 5, in <module>
from pkg_resources import load_entry_point
File "/usr/bin/lib/python2.7/site-packages/distribute-0.6.19-py2.7.egg/pkg_resources.py", line 2713, in <module>
parse_requirements(__requires__), Environment()
File "/usr/bin/lib/python2.7/site-packages/distribute-0.6.19-py2.7.egg/pkg_resources.py", line 584, in resolve
raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: pip==0.8.2
I've already install both of them (and yes, first deleted them), but no
result...
Thanks!
[(I tried already this
post)](http://stackoverflow.com/questions/5585473/upgraded-python-on-
snowleopard-using-homebrew-now-pip-and-easy-install-dont-work)
Answer: I had this issue where python's distribute package wasn't installed for some
reason. After following the instructions on [python-
distribute](https://web.archive.org/web/20100309145033/http://guide.python-
distribute.org/installation.html), i got it working.
install the distribute package as follows:
$ wget https://web.archive.org/web/20100225231201/http://python-distribute.org/distribute_setup.py
$ python distribute_setup.py
**EDIT:~~<http://python-distribute.org/distribute_setup.py>~~ no longer
works:**
hopefully this will resolve your problem with running
$ sudo easy_install
Happy Coding!
|
Python Read Formatted String
Question: I have a file with a number of lines formatted with the following syntax:
FIELD POSITION DATA TYPE
------------------------------
COOP ID 1-6 Character
LATITUDE 8-15 Real
LONGITUDE 17-25 Real
ELEVATION 27-32 Real
STATE 34-35 Character
NAME 37-66 Character
COMPONENT1 68-73 Character
COMPONENT2 75-80 Character
COMPONENT3 82-87 Character
UTC OFFSET 89-90 Integer
The data is all ASCII-formatted.
An example of a line is:
011084 31.0581 -87.0547 26.0 AL BREWTON 3 SSE ------ ------ ------ +6
My current thought is that I'd like to read the file in a line at a time and
_somehow_ have each line broken up into a dictionary so I can refer to the
components. Is there some module that does this in Python, or some other clean
way?
Thanks!
Answer: **EDIT** : You can still use the struct module:
See the [struct module](http://docs.python.org/library/struct.html)
documentation. Looks to me like you want to use `struct.unpack()`
What you want is probably something like:
import struct
with open("filename.txt", "r") as f:
for line in f:
(coop_id, lat, lon, elev, state, name, c1, c2, c3, utc_offset
) = struct.unpack("6sx8sx9sx6sx2sx30sx6sx6sx6sx2s", line.strip())
(lat, lon, elev) = map(float, (lat, lon, elev))
utc_offset = int(utc_offset)
|
Can't access collection from the shell - SyntaxError: missing ; before statement (shell):1
Question: I wrote a script that uses mongoimport to load csv files into mongodb. When I
run this for two similar csv files (of the same type) both upload fine,
however I can only access one of them from the mongodb shell. Here is a
transcript of a mongodb shell session:
> show collections
3mLgQAYJCq6_20110802
eTByWMY7zO6_20110802NonUniCode
system.indexes
> db.3mLgQAYJCq6_20110802
Thu Aug 18 18:44:49 SyntaxError: missing ; before statement (shell):1
> db.eTByWMY7zO6_20110802NonUniCode
vh.eTByWMY7zO6_20110802NonUniCode
However, I can access both collections from a python script and using
mongoexport. I suspect there is a problem with the 3mLgQAYJCq6_20110802 file
but I don't know where to start looking. Any ideas?
Answer: This works for me when my collection names include special characters:
db["3mLgQAYJCq6_20110802"].findOne();
|
NotImplementedException in Silverlight and IronPython
Question: i'm hosting IronPython Scripts in one Silverlight Application and i want to
run the script and get one System.Windows.Controls.TextBlock object.
so i use this ironPython code:
import clr
clr.AddReferenceByName("System.Windows.Controls, Version=2.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")
from System.Windows.Controls import *
tb = TextBlock()
i'm being able to add the reference, but, when i import
System.Windows.Controls i get a System.NotImplementedException.
The same happens if i try with "import wpf"
i'm using Silverlight 4 and IronPython 2.7.1 beta2 and this is the code to run
the script:
Dim engine = IronPython.Hosting.Python.CreateEngine
Dim scope = engine.CreateScope()
Dim source = engine.CreateScriptSourceFromString(CodeTB.Text)
source.Execute(scope)
ResultLB.Items.Add(scope.GetVariable("hello"))
If scope.ContainsVariable("tb") Then
GuiStack.Children.Add(scope.GetVariable("tb"))
End If
Here is the Stack Trace of the exception:
en Microsoft.Scripting.PlatformAdaptationLayer.FileExists(String path)
en IronPython.Runtime.Importer.LoadModuleFromSource(CodeContext context, String name, String path)
en IronPython.Runtime.Importer.LoadPackageFromSource(CodeContext context, String name, String path)
en IronPython.Runtime.Importer.LoadFromDisk(CodeContext context, String name, String fullName, String str)
en IronPython.Runtime.Importer.ImportFromPathHook(CodeContext context, String name, String fullName, List path, Func`5 defaultLoader)
en IronPython.Runtime.Importer.ImportFromPath(CodeContext context, String name, String fullName, List path)
en IronPython.Runtime.Importer.ImportTopAbsolute(CodeContext context, String name)
en IronPython.Runtime.Importer.ImportModule(CodeContext context, Object globals, String modName, Boolean bottom, Int32 level)
en IronPython.Modules.Builtin.__import__(CodeContext context, String name, Object globals, Object locals, Object fromlist, Int32 level)
en Microsoft.Scripting.Interpreter.FuncCallInstruction`7.Run(InterpretedFrame frame)
en Microsoft.Scripting.Interpreter.Interpreter.Run(InterpretedFrame frame)
en Microsoft.Scripting.Interpreter.LightLambda.Run7[T0,T1,T2,T3,T4,T5,T6,TRet](T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6)
en IronPython.Runtime.Importer.ImportLightThrow(CodeContext context, String fullName, PythonTuple from, Int32 level)
en IronPython.Runtime.Importer.Import(CodeContext context, String fullName, PythonTuple from, Int32 level)
en IronPython.Runtime.Operations.PythonOps.ImportStar(CodeContext context, String fullName, Int32 level)
en Microsoft.Scripting.Interpreter.ActionCallInstruction`3.Run(InterpretedFrame frame)
en Microsoft.Scripting.Interpreter.Interpreter.Run(InterpretedFrame frame)
en Microsoft.Scripting.Interpreter.LightLambda.Run2[T0,T1,TRet](T0 arg0, T1 arg1)
en IronPython.Compiler.PythonScriptCode.RunWorker(CodeContext ctx)
en IronPython.Compiler.PythonScriptCode.Run(Scope scope)
en IronPython.Compiler.RuntimeScriptCode.InvokeTarget(Scope scope)
en IronPython.Compiler.RuntimeScriptCode.Run(Scope scope)
en Microsoft.Scripting.SourceUnit.Execute(Scope scope, ErrorSink errorSink)
en Microsoft.Scripting.SourceUnit.Execute(Scope scope)
en Microsoft.Scripting.Hosting.ScriptSource.Execute(ScriptScope scope)
en TestApp2.MainPage.ExecuteButton_Click(Object sender, RoutedEventArgs e)
en System.Windows.Controls.Primitives.ButtonBase.OnClick()
en System.Windows.Controls.Button.OnClick()
en System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
en System.Windows.Controls.Control.OnMouseLeftButtonUp(Control ctrl, EventArgs e)
en MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)
And here is the all the [source code](http://bit.ly/qIfma3)
Thankyou for everything :)
Answer: It should work without any `AddReference`:
import clr
from System.Windows.Controls import TextBlock
tb = TextBlock()
|
Python dictionary get method in assignment
Question: All,
I'm looping over a dictionary and counting the values that occur. To do this,
I'm using the get method in the assignment statement for another dictionary.
This returns a syntax error "can't assign to function call"
counts = {}
mydict = {'a':[1,2,5], 'b': [1,2,10]}
for key,value in mydict.iteritems():
counts(value[1]) = counts.get(value[1], 0) + 1
Why would the assignment try to point to the function, rather than the return
value?
Answer:
counts = {}
mydict = {'a':[1,2,5], 'b': [1,2,10]}
for key,value in mydict.iteritems():
counts[value[1]] = counts.get(value[1], 0) + 1
You need brackets, not parenthesis, to get an item from a dictionary.
Also, You're doing this the hard way.
from collections import defaultdict
# automatically start each count at zero
counts = defaultdict(int)
# we only need the values, not the keys
for value in mydict.itervalues():
# add one to the count for this item
counts[value[1]] += 1
or
# only on Python 2.7 or newer
from collections import Counter
counts = Counter(value[1] for value in mydict.itervalues())
|
In Python, how can I get the file system of a given file path
Question: In python, given a directory or file path like /usr/local, I need to get the
file system where its available. In some systems it could be / (root) itself
and in some others it could be /usr.
I tried os.statvfs it doesnt help. Do I have to run the df command with the
path name and extract the file system from the output? Is there a better
solution?
Its for linux/unix platforms only.
Thanks
Answer: Here is a slightly modified version of a recipe found
[here](http://stackoverflow.com/questions/1138383/python-get-mount-point-on-
windows-or-linux). `os.path.realpath` was added so symlinks are handled
correctly.
import os
def getmount(path):
path = os.path.realpath(os.path.abspath(path))
while path != os.path.sep:
if os.path.ismount(path):
return path
path = os.path.abspath(os.path.join(path, os.pardir))
return path
|
python "help" function: printing docstrings
Question: Is there an option to print the output of help('myfun'). The behaviour I'm
seeing is that output is printed to std.out and the script waits for user
input (i.e. type 'q' to continue).
There must be a setting to set this to just dump docstrings.
Alternatively, if I could just dump the docstring PLUS the "def f(args):" line
that would be fine too.
Searching for "python help function" is comical. :) Maybe I'm missing some
nice pydoc page somewhere out there that explains it all?
Answer: To get exactly the help that's printed by `help(str)` into the variable
`strhelp`:
import pydoc
strhelp = pydoc.render_doc(str, "Help on %s")
Of course you can then easily print it without paging, etc.
|
Appending various strings between two delimeters in one string. python
Question: I've been stuck here a day. So I thought to ask the experts. I am reading
contents from a file which has data in form
|something|
|something else|
|something_1
something_2
someting_3|
|something blah blah|
.. and so on.. so as you guys figured it out.. the delimiter is '|' now.. I
want the output in following form |something| |something else|
|something_1_something_2_someting_3| |something blah blah| basically
everything between a delimiter in one string Any clues how to go about it
Programming language is Python
Answer:
import re
print re.findall(r"\|[^|]*\|", text)
If you haven't seen this before, its a regular expression. Basically you
describe a pattern in text that you are looking for. I recommend reading up on
it if you don't know them.
|
Python search and replace not replacing properly
Question: I have this script that needs to replace a file extension and it is not doing
so properly:
import os
import sys
#directory is the directory we will work from
directory = "C:\\Users\\joe\\Desktop"
os.chdir(directory)
whatToLookFor = ["Ca", "Cb", "Cd", "Ce", "Cf", "Cg", "Ch", "Ci", "Cj", "Ck", "Cl", "Cm", "Cn", "Co",
"Fa", "Fb", "Fc", "Fd", "Fe", "Ff", "Fg", "Fh", "Fi", "Fk", "Fl", "Fm", "Fn", "Fo",
"Fp", "Ga", "Gb", "Gc", "Gd", "Ge", "Gf", "Gg", "Gh", "Gi", "Gj", "Gk", "Gn", "Ja",
"Jb", "Jc", "Jd", "Je", "Jf", "Jg", "Jh", "Jk", "Jl", "Jm", "Fj", "cc", "cb", "cd",
"ce", "cf", "cg", "ch", "ci", "cj", "ck", "cl", "cm", "cn", "co", "fa", "fb", "fc",
"fd", "fe", "ff", "fg", "fh", "fi", "fk", "fl", "fm", "fn", "fo", "fp", "ga", "gb",
"gc", "gd", "ge", "gf", "gg", "gh", "gi", "gj", "gk", "gn", "ja", "jb", "jc", "jd",
"je", "jf", "jg", "jh", "jk", "jl", "jm", "fj"]
oldFile = open("links.htm", "r")
newFile = open("python test.htm", "w")
buffer = oldFile.read()
for item in whatToLookFor:
for x in range(0, 80):
if x < 10:
buffer = buffer.replace(item + str(x), item.upper() + "-0" + str(x))
else:
buffer = buffer.replace(item + str(x), item.upper() + "-" + str(x))
newFile.write(buffer)
oldFile.close()
newFile.close()
The file ff10 is being changed to FF-010 when it should not be. It should be
changed to FF-10
Answer: Without knowing what your actual input is, it will be very difficult to help,
however, I did notice one thing. It looks like you are trying to make sure you
have two digit numbers in your buffer (after the item from whatToLookFor).
If that's true, life would probably be easier if you replaced this:
if x < 10:
buffer = buffer.replace(item + str(x), item.upper() + "-0" + str(x))
else:
buffer = buffer.replace(item + str(x), item.upper() + "-" + str(x))
With:
sx = str(x)
tmp = sx if len(sx) >= 2 else "0" + sx
buffer = buffer.replace(item + sx, item.upper()+ "-" + tmp)
Or, even better:
buffer = buffer.replace(item + str(x), "%s-%02d" % (item.upper(), int(x)) )
|
python: unpack IBM 32-bit float point
Question: I was reading a binary file in python like this:
from struct import unpack
ns = 1000
f = open("binary_file", 'rb')
while True:
data = f.read(ns * 4)
if data == '':
break
unpacked = unpack(">%sf" % ns, data)
print str(unpacked)
when I realized `unpack(">f", str)` is for unpacking IEEE floating point, my
data is IBM 32-bit float point numbers
My question is: How can I impliment my `unpack` to unpack IBM 32-bit float
point type numbers?
I don't mind using like `ctypes` to extend python to get better performance.
EDIT: I did some searching: <http://mail.scipy.org/pipermail/scipy-
user/2009-January/019392.html>
This looks very promising, but I want to get more efficient: there are
potential tens of thousands of loops.
EDIT: posted answer below. Thanks for the tip.
Answer: I think I understood it: first unpack the string to unsigned 4 byte integer,
and then use this function:
def ibm2ieee(ibm):
"""
Converts an IBM floating point number into IEEE format.
:param: ibm - 32 bit unsigned integer: unpack('>L', f.read(4))
"""
if ibm == 0:
return 0.0
sign = ibm >> 31 & 0x01
exponent = ibm >> 24 & 0x7f
mantissa = (ibm & 0x00ffffff) / float(pow(2, 24))
return (1 - 2 * sign) * mantissa * pow(16, exponent - 64)
Thanks for all who helped!
IBM Floating Point Architecture, how to encode and decode:
<http://en.wikipedia.org/wiki/IBM_Floating_Point_Architecture>
**My solution:** I wrote a class, I think in this way, it can be a bit faster,
because used Struct object, so that the unpack fmt is compiled only once.
EDIT: also because it's unpacking size*bytes all at once, and unpacking can be
an expensive operation.
from struct import Struct
class StructIBM32(object):
"""
see example in:
http://en.wikipedia.org/wiki/IBM_Floating_Point_Architecture#An_Example
>>> import struct
>>> c = StructIBM32(1)
>>> bit = '11000010011101101010000000000000'
>>> c.unpack(struct.pack('>L', int(bit, 2)))
[-118.625]
"""
def __init__(self, size):
self.p24 = float(pow(2, 24))
self.unpack32int = Struct(">%sL" % size).unpack
def unpack(self, data):
int32 = self.unpack32int(data)
return [self.ibm2ieee(i) for i in int32]
def ibm2ieee(self, int32):
if int32 == 0:
return 0.0
sign = int32 >> 31 & 0x01
exponent = int32 >> 24 & 0x7f
mantissa = (int32 & 0x00ffffff) / self.p24
return (1 - 2 * sign) * mantissa * pow(16, exponent - 64)
if __name__ == "__main__":
import doctest
doctest.testmod()
|
Standard error in non-linear regression
Question: I have been doing some Monte Carlo physics simulations with Python and I am in
unable to determine the standard error for the coefficients of a non-linear
least square fit.
Initially, I was using SciPy's `scipy.stats.linregress` for my model since I
thought it would be a linear model but noticed it is actually some sort of
power function. I then used NumPy's `polyfit` with the degrees of freedom
being 2 but I can't find anyway to determine the standard error of the
coefficients.
I know gnuplot can determine the errors for me but I need to do fits for over
30 different cases. I was wondering if anyone knows of anyway for Python to
read the standard error from gnuplot or is there some other library I can use?
Answer: Finally found the answer to this long asked question! I'm hoping this can at
least save someone a few hours of hopeless research for this topic. Scipy has
a special function called curve_fit under its optimize section. It uses the
least square method to determine the coefficients and best of all, it gives
you the covariance matrix. The covariance matrix contains the variance of each
coefficient. More exactly, the diagonal of the matrix is the variance and by
square rooting the values, the standard error of each coefficient can be
determined! Scipy doesn't have much documentation for this so here's a sample
code for a better understanding:
import numpy as np
from scipy.optimize import curve_fit
import matplotlib.pyplot as plot
def func(x,a,b,c):
return a*x**2 + b*x + c #Refer [1]
x = np.linspace(0,4,50)
y = func(x,2.6,2,3) + 4*np.random.normal(size=len(x)) #Refer [2]
coeff, var_matrix = curve_fit(func,x,y)
variance = np.diagonal(var_matrix) #Refer [3]
SE = np.sqrt(variance) #Refer [4]
#======Making a dictionary to print results========
results = {'a':[coeff[0],SE[0]],'b':[coeff[1],SE[1]],'c':[coeff[2],SE[2]]}
print "Coeff\tValue\t\tError"
for v,c in results.iteritems():
print v,"\t",c[0],"\t",c[1]
#========End Results Printing=================
y2 = func(x,coeff[0],coeff[1],coeff[2]) #Saves the y values for the fitted model
plot.plot(x,y)
plot.plot(x,y2)
plot.show()
1. What this function returns is critical because it defines what will used to fit for the model
2. Using the function to create some arbitrary data + some noise
3. Saves the covariance matrix's diagonal to a 1D matrix which is just a normal array
4. Square rooting the variance to get the standard error (SE)
|
Text similarity algorithm, optimization concerns
Question: I have a django blog, and I am writing a simple similiar text algorithm for
it. The code below is the code that I tested with a copy of my blog's
database. (Note: code was originally in Turkish, I changed variable names to
English for convenience. Therefore, things may look weird.)
# -*- coding:utf-8 -*-
from django.utils.html import strip_tags
import os
import sys
import math
import re
PROJECT_FOLDER = os.path.abspath(os.path.dirname(__file__))
UPPER_FOLDER = os.path.abspath(PROJECT_FOLDER + "/../")
sys.path.append(UPPER_FOLDER)
os.environ["DJANGO_SETTINGS_MODULE"] = "similarity.settings"
from blog.models import Post
def getWords(post_object):
all = post_object.title + " " + post_object.abstract + " " + post_object.post
all = strip_tags(all.lower())
regex = re.compile("\W+",flags=re.UNICODE)
return re.split(regex,all)
def count_things(what_to_count,the_set):
num = 0
for the_thing in the_set:
if what_to_count in the_thing[1]:
num += 1
return num
a = Post.objects.all()
b = []
for post in a:
b.append((post.title,getWords(post)))
del(a)
def adjustWeight(the_list,the_word):
numOccr = the_list.count(the_word)
if numOccr == 0:
return 0
else:
return math.log(numOccr,1.6)
results = []
uniques = []
for i in range(0,len(b)):
for a_word in b[i][1]:
if a_word not in uniques:
uniques.append(a_word)
for i in range(1,len(b)):
for j in range(0,i):
upper_part = 0
sum1 = 0
sum2 = 0
for a_word in uniques:
adjusted1 = adjustWeight(b[i][1],a_word)
adjusted2 = adjustWeight(b[j][1],a_word)
upper_part += adjusted1 * adjusted2 * math.log(len(b)/count_things(a_word,b))
sum1 += adjusted1
sum2 += adjusted2
lower_part = math.sqrt(sum1 * sum2)
results.append((b[i][0], b[j][0], upper_part/lower_part))
results = sorted(results, key = lambda x: x[2])
results.reverse()
print("\n".join(["%s and %s => %f" % (x,c,v) for x,c,v in results]).encode("utf-8"))
What it does, in a nutshell is, compare all possible pairs and outputs a
similarity report. Now what I want is to merge this with my blog. However,
this is a very expensive code, so need some optimazing. This is what I have in
mind.
I will have a cron job for a python file, where it compares newly added or
modified texts with all other texts, and store similarity scores in database
for use.
Another thing I have in mind is, open another table and made some indexing on
it like this: "post id" "word" "number of occurence", so instead of reading
the post, counting the words everytime, I would just read that data from
database, in which everything is already done.
I was wondering what do you thing about this. I wanted to get idea of others
since I am not expert on the issue.
Answer: If you want to do text similarity based searching, you are better off going
with a search server like Sphinx: <http://sphinxsearch.com/>
|
BeautifulSoup installed but not recognized when dev_appserver runs
Question: **Update**
By adding BeautifulSoup.py to my app source, this error was gone :)
Thanks @Ned Deily, that took along time, but was fruitful
_**Ignore from here_**
I have just one instance of python 2.5 installed with BeautifulSoup, still no
luck!, what I am I doing wrong, please help
bash-3.2$ ls -ltr /Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages
total 1096
-rw-r--r-- 1 Harit admin 66866 May 28 2006 BeautifulSoup.py
-rw-r--r-- 1 Harit admin 26413 May 28 2006 BeautifulSoupTests.py
-rw-rwxr-- 1 root admin 119 Sep 18 2006 README
drwxr-xr-x 19 Harit admin 646 Aug 20 23:58 django
-rw-r--r-- 1 Harit admin 1228 Aug 20 23:58 Django-1.3-py2.5.egg-info
-rw-r--r-- 1 Harit admin 333390 Aug 21 00:17 setuptools-0.6c11-py2.5.egg
-rw-r--r-- 1 Harit admin 30 Aug 21 00:17 setuptools.pth
-rw-r--r-- 1 Harit admin 215 Aug 21 00:22 easy-install.pth
-rw-r--r-- 1 Harit admin 33196 Aug 21 00:23 BeautifulSoupTests.pyc
-rw-r--r-- 1 Harit admin 67193 Aug 21 00:23 BeautifulSoup.pyc
-rw-r--r-- 1 Harit admin 970 Aug 21 00:23 BeautifulSoup-3.0.0-py2.5.egg-info
bash-3.2$
_**Ignore from here_**
I removed all versions of python from macport and system and re installed the
python 2.7 version
bash-3.2$ python
Python 2.7.2 (v2.7.2:8527427914a2, Jun 11 2011, 15:22:34)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import django
>>> from BeautifulSoup import BeautifulSoup
>>>
and all the paths also look good
bash-3.2$ echo $PATH
/Library/Frameworks/Python.framework/Versions/2.7/bin:/opt/local/bin:/opt/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/git/bin:/usr/X11/bin:/opt/local/bin
and have just one version of python that has both `Django` and `BeautifulSoup`
installed
bash-3.2$ cd /Library/Frameworks/Python.framework/Versions/Current/
Headers/ Mac/ Python Resources/ bin/ include/ lib/ share/
bash-3.2$ cd /Library/Frameworks/Python.framework/Versions/Current/lib/python2.7/lib
lib-dynload/ lib-tk/ lib2to3/
bash-3.2$ cd /Library/Frameworks/Python.framework/Versions/Current/lib/python2.7/
Display all 641 possibilities? (y or n)
bash-3.2$ ls /Library/Frameworks/Python.framework/Versions/Current/lib/python2.7/site-packages/
BeautifulSoup-3.2.0-py2.7.egg-info BeautifulSoupTests.pyc easy-install.pth
BeautifulSoup.py Django-1.3-py2.7.egg-info setuptools-0.6c11-py2.7.egg
BeautifulSoup.pyc README setuptools.pth
BeautifulSoupTests.py django
bash-3.2$
but still when I run `dev_appserver.py project` it says it can not import
module `BeautifulSoup`
Please help
Thank you
_**Ignore from below_**
I have BeautifulSoup installed on my mac and I can do the following:
bash-3.2$ python
Python 2.6.7 (r267:88850, Jul 27 2011, 11:54:59)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from BeautifulSoup import BeautifulSoup
>>>
but when I run my djando app and try to run the code, it fails saying
Error was: No module named BeautifulSoup
It seems I am using everything correctly
bash-3.2$ which python
/opt/local/bin/python
lrwxr-xr-x 1 root admin 9 Aug 16 13:55 python -> python2.6
bash-3.2$ cd /Library/Python/2.6/site-packages/
BeautifulSoup-3.0.0-py2.6.egg-info ipython-0.11-py2.6.egg/
BeautifulSoup.py mercurial/
BeautifulSoup.pyc mercurial-1.8.3_20110502-py2.6.egg-info/
BeautifulSoupTests.py nose-1.1.2-py2.6.egg/
BeautifulSoupTests.pyc paramiko-1.7.6-py2.6.egg
Django-1.3-py2.6.egg-info pip-1.0.2-py2.6.egg/
MySQL_python-1.2.3-py2.6-macosx-10.6-universal.egg pycrypto-2.3-py2.6-macosx-10.6-universal.egg
README pysqlite-2.6.3-py2.6.egg-info
django/ pysqlite2/
easy-install.pth setuptools-0.6c11-py2.6.egg
easy_install setuptools.pth
easy_install-2.6 xlrd/
hgext/ xlrd-0.6.1-py2.6.egg-info
How can I resolve this issue
Thanks
Answer: You apparently have installed a second, newer instance of Python 2.6. Chances
are that your Django app is installed and being run from another instance of
Python 2.6, possibly the system Python 2.6 (`/usr/bin/python` or
`/usr/bin/python2.6`). Type `which python` to see the path of the Python which
has BeautifulSoup (`/usr/local/bin/python` perhaps?). You'll need to
consolidate things; either install BeautifulSoup in the Python with Django or
install Django in the Python with BeautifulSoup.
UPDATE: Since you are apparently running the Google App Engine dev_server,
chances are that it is running under Python 2.5, not Python 2.6; at the
moment, GAE is officially supported only with 2.5, as far as I know. Note
Apple ships both a Python 2.6 and 2.5 with OS X 10.6. So you probably need to
install Beautiful Soup in Python 2.5. Try:
easy_install-2.5 -U -v beautifulsoup==3.2
At the moment, you'll need to specify the version as there is currently a
newer beta version of Beautiful Soup 4 that appears to be incompatible with
Python 2.5.
UPDATE: You also seem to have more than one version of Python 2.5 installed.
The path you show is for a 3rd-party Python, not the Apple-supplied Python
2.5. _So_ my final suggestion is to try using the easy_install-2.5 for the
Apple-supplied Python 2.5:
/usr/bin/easy_install-2.5 -U -v beautifulsoup==3.2
|
Python For Loop Slowing With Time
Question: So I'm having a little trouble dealing with for loops in Python - as far as I
can tell, they're getting slower with time. I'm looping over a range inside of
a range, and as time passes, the loop noticeably slows. This is done inside of
a game engine, if it matters. Could anyone tell me what the issue is?
Here's a quick example.
for x in range(xs): # xs, ys, and zs are all pre-determined size values
for z in range(zs):
for y in range(ys):
vp = [x * vs, y * vs, z * vs]
v = Cube(vp)
The initial speed of this process is fine, but with time the loop slows. I
know it's not anything else like the Rasterizer of the game engine because
when the loop is done, the rest of the engine runs at 60 FPS. So what could be
the problem?
EDIT: I'm using Python 3, so there is no xrange.
EDIT 2: For this example, vs is 1.0, and the predetermined size values of xs,
ys, and zs are all 20.
Answer: This is another case of "need more information". However, Python has a
standard way of constructing nested loops like this efficiently,
[`itertools.product`](http://docs.python.org/library/itertools.html#itertools.product):
from itertools import product
for x, y, z in product(xrange(xs), xrange(zs), xrange(ys)):
vp = [x * vs, y * vs, z * vs]
v = Cube(vp)
It doesn't require the construction of `range`s every time in the inner loop.
I also switched your use of `range` to `xrange`, as it's better for large
ranges, although this is really irrelevant with `product`.
@JohnZ's question is good -- if your "predetermined size values" are very
large, and especially if `vs` is also large, you could be constructing some
large values, and it could be taking a long time for `Cube` to process them.
I doubt the loop itself is slowing down, but the numbers are getting larger,
so your calculations might be.
|
Average of large number of Dice Rolls in Haskell
Question: In an attempt to learn Haskell better, I'm trying to write a program that
displays the average value of the sum of 2 die, rolled X number of times. This
is fairly simple in C, Java, Python... but I'm stuck in Haskell. Here's a
naive attempt:
import System.Random
main = do
g <- getStdGen
let trials = 10000000
let rolls = take trials (randomRs (2, 12) g :: [Int])
let average = div (sum rolls) trials
print average
For low number of trials, the program works. But when I run this code with ten
million trials, I get an error:
Stack space overflow: current size 8388608 bytes.
Use `+RTS -Ksize -RTS' to increase it.
There's got to be a better way to write this program. In the C, Java, and
Python versions, this is a simple task. I've looked at
[this](http://stackoverflow.com/questions/2110535/sampling-sequences-of-
random-numbers-in-haskell) post (and understand about 75% of the material),
but when I adapt that code to this situation, summing a sequence of `R [Int]`
doesn't work (and I'm not sure how to 'unwrap' the [Int]). What am I doing
wrong? What's the right way? How do I reach random number enlightenment in
Haskell?
**Edit:** in addition to the answer selected, as rtperson points out below,
the modeling of 2 dice is incorrect; it should really be the sum of two
independent rolls from 1 to 6.
Answer: `sum` is no good to sum a long list, it runs in linear space. Try this strict
version of `sum`:
sum' = foldl' (+) 0
`foldl'` is defined in `Data.List`.
**EDIT** More information can be found in [this HaskellWiki
article](http://www.haskell.org/haskellwiki/Foldr_Foldl_Foldl%27).
|
Python win32com - Read text in a text box to a cell?
Question: I would like to read the text from a text box in an Excel File and save that
value to a variable. The problem I am having is with the reading of the
TextBox. I have tried several methods, this one showed the most promise, as it
does not generate an error, but it does not elicit the desired result either.
Any suggestions are appreciated. See code below.
import win32com.client as win32
excel = win32.gencache.EnsureDispatch('Excel.Application')
wb = excel.Workbooks.Open("C:\\users\\khillstr\\Testing\\Scripts\\Book1.xlsx")
excel.Visible = False
ws = wb.Worksheets
canvas = excel.ActiveSheet.Shapes
for shp in canvas.CanvasItems:
if shp.TextFrame.Characters:
print shp.TextFrame.Characters
else:
print "no"
Answer: Canvas has to do with graphics in excel files. I think you want access to the
cells. Below is code that prints out each row as a tuple.
import win32com.client as win32
excel = win32.gencache.EnsureDispatch('Excel.Application')
wb = excel.Workbooks.Open("C:\\users\\khillstr\\Testing\\Scripts\\Book1.xlsx")
excel.Visible = False
sheet = wb.Worksheets(1)
for row in sheet.UsedRange.Value:
print row
|
program timeout in windows for python
Question: Hi I've seen a bunch of questions here on SE that deal with similar issues but
I find much of the answers to be unclear and confusing. My question is very
simple. How on a Windows platform can I kill a running function after a
certain amount of time using Python v2.6? If I have:
def my_function(start):
x=start
while True:
print x
x=x+1
return x
how can I have this stop after X seconds? Please keep your answers clear about
where to put in my function and how to adjust the time limit. Thanks
Answer: If you just want to run a normal function with a timeout, try:
from datetime import timedelta, datetime
from time import sleep
endtime = datetime.utcnow() + timedelta(seconds = 2)
while True:
sleep(1) # just an example
if datetime.utcnow() > endtime: # if more than two seconds has elapsed
break
If you're talking about stopping a thread, there is a blog post about doing
this with threads which covers all the bases.
[How (not) to set a timeout on a computation in
Python](http://eli.thegreenplace.net/2011/08/22/how-not-to-set-a-timeout-on-a-
computation-in-python/). The [author](http://stackoverflow.com/users/8206/eli-
bendersky) also uses this site.
Basically, the answer is that there is no "right way" to do this in Python,
though if you're not on Windows `SIGALARM` works.
|
using python subprocess call to invoke python script
Question: I have a python script that needs to invoke another python script in the same
directory. I did this:
from subprocess import call
call('somescript.py')
I get the following error
call('somescript.py')
File "/usr/lib/python2.6/subprocess.py", line 480, in call
return Popen(*popenargs, **kwargs).wait()
File "/usr/lib/python2.6/subprocess.py", line 633, in __init__
errread, errwrite)
File "/usr/lib/python2.6/subprocess.py", line 1139, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory
I have the script somescript.py in the same folder though. Am i missing
something here. Thanks
Answer: If 'somescript.py' isn't something you could normally execute directly from
the command line (I.E. `$: somescript.py` works), then you can't call it
directly using call.
Remember that the way Popen works is that the first argument is the program
that it executes, and the rest are the arguments passed to that program. In
this case, the program is actually _python_ , not your script. So the
following will work as you expect:
subprocess.call(['python', 'somescript.py', somescript_arg1, somescript_val1,...]).
This correctly calls the python interpreter and tells it to execute your
script with the given arguments.
Note that this is different from the above suggestion:
subprocess.call(['python somescript.py'])
That will try to execute the program called _python somscript.py_ , which
clearly doesn't exist.
call('python somescript.py', shell=True)
Will also work, but using strings as input to call is not cross platform, is
dangerous if you aren't the one building the string, and should generally be
avoided if at all possible.
|
Help calculating Avg and std for excel files saved as CSV
Question: I have about 20 excel files saved as CSV in a single folder. Each excel file
has numbers saved in the first, second and third columns. I was trying to read
the first column for all of the files, second column for all of the file, and
third column for all of the files using CSV module in python, and calulate the
average and standard deviation for each column and save these results in a
single separate excel. please help.... this is what i have so far...how can i
access each column separately?
import csv
import os
from numpy import array
path="A:\\hello\\folder"
dirList=os.listdir(path)
for file in dirList:
fullpath=os.path.join(path,file)
## print fullpath
with open(fullpath, 'rb') as f:
[[val for val in line.split(',')] for line in f.readlines()]
## print line
nums = array([line])
for row in nums:
print row.mean()
Answer: A [**list
comprehension**](http://docs.python.org/tutorial/datastructures.html#list-
comprehensions) works kinda like a backwards for-loop that automatically
constructs a `list` for you. If you nest these with the "columns" on the
inside and the "rows" on the outside you should get a matrix thingy (nested
list structure):
nums = [[int(val) for val in line.split(',')] for line in my_file.readlines()]
Or maybe if you have a csv reader object it might be like this:
nums = [[int(val) for val in line] for line in my_csv_reader]
And now you've got your matrix in a variable called `nums` thanks to the above
_list comprehension_.
Then you should probably use [numpy](http://new.scipy.org/download.html) to
compute your stats. This is nice because you can access columns of a numpy
array very easily and when you do it returns the column in the form of a numpy
array. numpy arrays also happen to have built-in methods for mean and standard
deviation. You can cast your `nums` to a numpy array just by passing it into
the `array()` constructor function :
from numpy import array
anums = array(nums)
Then if you want to iterate through columns, use the array slice notation and
the `shape` variable that is a member of every numpy array:
# The 1 index of anums.shape should tell you how many columns you have
for c in range(anums.shape[1]):
column = anums[:,c]
col_mean = column.mean()
col_std = column.std()
# Do something with these variables here, probably
|
Problem importing matplotlib.mlab and .pyplot in python 2.7 on Mac OSX 10.6
Question: I am trying to plot a histogram using matplotlib in Python 2.7 on OSX 10.6
I have verified that I can import numpy, scipy, and matplotlib into python. A
sample script on the matplotlib website does
#!/usr/bin/env python
import numpy as np
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
However, I get an error when doing this. Here is what happens when I try to
import mlab.
Python 2.7.2 (v2.7.2:8527427914a2, Jun 11 2011, 15:22:34)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import matplotlib.mlab as mlab
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/mlab.py", line 151, in <module>
import matplotlib.nxutils as nxutils
ImportError: dlopen(/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/nxutils.so, 2): no suitable image found. Did find:
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/nxutils.so: no matching architecture in universal wrapper
>>>
What am I doing wrong that I can't import these as the script does?
Answer: For the _ImportError_ : It seems that there is an architecture mismatch. Maybe
you have installed a 32-bit version of matplotlib, but are using a 64-bit
Python? What does the following shell command print?
file /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/nxutils.so
For the _AttributeError_ : You have to explicitely import `matplotlib.pyplot`,
it won't get imported automatically when just importing `matplotlib`. The most
common aliasing scheme is:
import numpy as np
import matplotlib as mpl
import matplotlib.pyplot as plt
Then you can draw your histogram using the `plt` name:
plt.hist(...)
|
Renaming filenames using python
Question: I need to simply add the word "_Manual" onto the end of all the files i have
in a specific directory Here is the script i am using at the moment - i have
no experience with python so this script is a frankenstine of other scripts i
had lying around!
It doesn't give any error messages but it also doesnt work..
folder = "C:\Documents and Settings\DuffA\Bureaublad\test"
import os, glob
for root, dirs, filenames in os.walk(folder):
for filename in filenames:
filename_split = os.path.splitext(filename) # filename and extensionname (extension in [1])
filename_zero = filename_split[0]
os.rename(filename_zero, filename_zero + "_manual")
I am now using
folder = "C:\Documents and Settings\DuffA\Bureaublad\test"
import os # glob is unnecessary
for root, dirs, filenames in os.walk(folder):
for filename in filenames:
fullpath = os.path.join(root, filename)
filename_split = os.path.splitext(fullpath) # filename and extensionname (extension in [1])
filename_zero, fileext = filename_split
print fullpath, filename_zero + "_manual" + fileext
os.rename(fullpath, filename_zero + "_manual" + fileext)
but it still doesnt work.. it doesnt print anything and nothing gets changed
in the folder!
Answer: `os.rename` requires a source and destination filename. The variable
`filename` contains your current filename (e.g., "something.txt"), whereas
your split separates that into `something` and `txt`. As the source file to
rename, you then only specify `something`, which fails silently.
Instead, you want to rename the file given in `filename`, but as you walk into
subfolders as well, you need to make sure to use the absolute path. For this
you can use `os.path.join(root, filename)`.
So in the end you get something like this:
os.rename(os.path.join(root, filename),
os.path.join(root, filename_zero + "_manual" + filename_split[1]))
This would rename `dir1/something.txt` into `dir1/something_manual.txt`.
|
pass session cookies in http header with python urllib2?
Question: I'm trying to write a simple script to log into Wikipedia and perform some
actions on my user page, using the Mediawiki api. However, I never seem to get
past the first login request (from this page:
<https://secure.wikimedia.org/wikipedia/en/wiki/Wikipedia:Creating_a_bot#Logging_in>).
I don't think the session cookie that I set is being sent. This is my code so
far:
import Cookie, urllib, urllib2, xml.etree.ElementTree
url = 'https://secure.wikimedia.org/wikipedia/en/w/api.php?action=login&format=xml'
username = 'user'
password = 'password'
user_data = [('lgname', username), ('lgpassword', password)]
#Login step 1
#Make the POST request
request = urllib2.Request(url)
data = urllib.urlencode(user_data)
login_raw_data1 = urllib2.urlopen(request, data).read()
#Parse the XML for the login information
login_data1 = xml.etree.ElementTree.fromstring(login_raw_data1)
login_tag = login_data1.find('login')
token = login_tag.attrib['token']
cookieprefix = login_tag.attrib['cookieprefix']
sessionid = login_tag.attrib['sessionid']
#Set the cookies
cookie = Cookie.SimpleCookie()
cookie[cookieprefix + '_session'] = sessionid
#Login step 2
request = urllib2.Request(url)
session_cookie_header = cookieprefix+'_session='+sessionid+'; path=/; domain=.wikipedia.org; HttpOnly'
request.add_header('Set-Cookie', session_cookie_header)
user_data.append(('lgtoken', token))
data = urllib.urlencode(user_data)
login_raw_data2 = urllib2.urlopen(request, data).read()
I think the problem is somewhere in the `request.add_header('Set-Cookie',
session_cookie_header)` line, but I don't know for sure. How do I use these
python libraries to send cookies in the header with every request (which is
necessary for a lot of API functions).
Answer: The latest version of [`requests`](http://docs.python-
requests.org/en/latest/index.html) has support for
[sessions](http://docs.python-requests.org/en/latest/user/advanced/#session-
objects) (as well as being really simple to use and generally great):
with requests.session() as s:
s.post(url, data=user_data)
r = s.get(url_2)
|
Using Python Iterparse For Large XML Files
Question: I need to write a parser in Python that can process some extremely large files
( > 2 GB ) on a computer without much memory (only 2 GB). I wanted to use
iterparse in lxml to do it.
My file is of the format:
<item>
<title>Item 1</title>
<desc>Description 1</desc>
</item>
<item>
<title>Item 2</title>
<desc>Description 2</desc>
</item>
and so far my solution is:
from lxml import etree
context = etree.iterparse( MYFILE, tag='item' )
for event, elem in context :
print elem.xpath( 'description/text( )' )
del context
Unfortunately though, this solution is still eating up a lot of memory. I
think the problem is that after dealing with each "ITEM" I need to do
something to cleanup empty children. Can anyone offer some suggestions on what
I might do after processing my data to properly cleanup?
Answer: Try [Liza Daly's
fast_iter](http://www.ibm.com/developerworks/xml/library/x-hiperfparse/).
After processing an element, `elem`, it calls `elem.clear()` to remove
descendants and also removes preceding siblings.
def fast_iter(context, func, *args, **kwargs):
"""
http://lxml.de/parsing.html#modifying-the-tree
Based on Liza Daly's fast_iter
http://www.ibm.com/developerworks/xml/library/x-hiperfparse/
See also http://effbot.org/zone/element-iterparse.htm
"""
for event, elem in context:
func(elem, *args, **kwargs)
# It's safe to call clear() here because no descendants will be
# accessed
elem.clear()
# Also eliminate now-empty references from the root node to elem
for ancestor in elem.xpath('ancestor-or-self::*'):
while ancestor.getprevious() is not None:
del ancestor.getparent()[0]
del context
def process_element(elem):
print elem.xpath( 'description/text( )' )
context = etree.iterparse( MYFILE, tag='item' )
fast_iter(context,process_element)
Daly's article is an excellent read, especially if you are processing large
XML files.
* * *
Edit: The `fast_iter` posted above is a modified version of Daly's
`fast_iter`. After processing an element, it is more aggressive at removing
other elements that are no longer needed.
The script below shows the difference in behavior. Note in particular that
`orig_fast_iter` does not delete the `A1` element, while the `mod_fast_iter`
does delete it, thus saving more memory.
import lxml.etree as ET
import textwrap
import io
def setup_ABC():
content = textwrap.dedent('''\
<root>
<A1>
<B1></B1>
<C>1<D1></D1></C>
<E1></E1>
</A1>
<A2>
<B2></B2>
<C>2<D></D></C>
<E2></E2>
</A2>
</root>
''')
return content
def study_fast_iter():
def orig_fast_iter(context, func, *args, **kwargs):
for event, elem in context:
print('Processing {e}'.format(e=ET.tostring(elem)))
func(elem, *args, **kwargs)
print('Clearing {e}'.format(e=ET.tostring(elem)))
elem.clear()
while elem.getprevious() is not None:
print('Deleting {p}'.format(
p=(elem.getparent()[0]).tag))
del elem.getparent()[0]
del context
def mod_fast_iter(context, func, *args, **kwargs):
"""
http://www.ibm.com/developerworks/xml/library/x-hiperfparse/
Author: Liza Daly
See also http://effbot.org/zone/element-iterparse.htm
"""
for event, elem in context:
print('Processing {e}'.format(e=ET.tostring(elem)))
func(elem, *args, **kwargs)
# It's safe to call clear() here because no descendants will be
# accessed
print('Clearing {e}'.format(e=ET.tostring(elem)))
elem.clear()
# Also eliminate now-empty references from the root node to elem
for ancestor in elem.xpath('ancestor-or-self::*'):
print('Checking ancestor: {a}'.format(a=ancestor.tag))
while ancestor.getprevious() is not None:
print(
'Deleting {p}'.format(p=(ancestor.getparent()[0]).tag))
del ancestor.getparent()[0]
del context
content = setup_ABC()
context = ET.iterparse(io.BytesIO(content), events=('end', ), tag='C')
orig_fast_iter(context, lambda elem: None)
# Processing <C>1<D1/></C>
# Clearing <C>1<D1/></C>
# Deleting B1
# Processing <C>2<D/></C>
# Clearing <C>2<D/></C>
# Deleting B2
print('-' * 80)
"""
The improved fast_iter deletes A1. The original fast_iter does not.
"""
content = setup_ABC()
context = ET.iterparse(io.BytesIO(content), events=('end', ), tag='C')
mod_fast_iter(context, lambda elem: None)
# Processing <C>1<D1/></C>
# Clearing <C>1<D1/></C>
# Checking ancestor: root
# Checking ancestor: A1
# Checking ancestor: C
# Deleting B1
# Processing <C>2<D/></C>
# Clearing <C>2<D/></C>
# Checking ancestor: root
# Checking ancestor: A2
# Deleting A1
# Checking ancestor: C
# Deleting B2
study_fast_iter()
|
pyodbc returns SQL Server DATE fields as strings
Question: I'm using pyodbc to query a SQL Server 2008 database table with columns of
DATE type.
The resulting rows of data contain date strings rather than python
datetime.date or datetime.datetime instances.
**This only appears to be an issue for columns of type DATE; columns of type
DATETIME are handled correctly and return a datetime.datetime instance.**
## Example
import pyodbc
from pprint import pformat
db = pyodbc.connect("DRIVER={SQL Server};SERVER=.\\SQLEXPRESS;DATABASE=scratch;Trusted_Connection=yes")
print pformat(db.cursor().execute("select * from Contract").description)
Results:
(('id', <type 'int'>, None, 10, 10, 0, False),
('name', <type 'str'>, None, 23, 23, 0, False),
('some_date', <type 'unicode'>, None, 10, 10, 0, True),
('write_time', <type 'datetime.datetime'>, None, 23, 23, 3, False))
Note that the **some_date** column is indicated as type unicode string,
however, in the database this column is defined as DATE:
CREATE TABLE dbo.Contract(
id INT NOT NULL,
name VARCHAR(23) NOT NULL,
some_date DATE NULL,
write_time DATETIME NOT NULL)
Is this normal, and how can I best correct it?
Answer: Use the SQL Server native client. e.g. Put **Driver={SQL Server Native Client
10.0}** in your connection string,instead of **DRIVER={SQL Server}**.
Reproduced your scenario with date being returned as string using SQL Server
ODBC driver. When using a 2008+ compatible version of the SQL Server native
client, the date type is returned as expected, but it looks like datetime2
gets returned as string (in my limited testing).
Table definition:
create table dbo.datetest (
[date] date not null,
[datetime] datetime not null,
[datetime2] datetime2 not null
);
insert into
dbo.datetest
values
(CAST(current_timestamp as DATE),
CAST(current_timestamp as datetime),
CAST(current_timestamp as datetime2));
Example:
import pyodbc
from pprint import pformat
db = pyodbc.connect(driver='{SQL Server Native Client 10.0}',
server='TESTSRVR', database='TESTDB',
trusted_connection='yes')
print pformat(db.cursor().execute("select * from dbo.datetest").description)
Results:
(('date', <type 'datetime.date'>, None, 10, 10, 0, False),
('datetime', <type 'datetime.datetime'>, None, 23, 23, 3, False),
('datetime2', <type 'unicode'>, None, 27, 27, 0, False))
|
Python mail: encoded attachments are truncated
Question: I'm using the following function to send an email message with two attachments
in my python script:
import smtplib
from email.MIMEMultipart import MIMEMultipart
from email.MIMEBase import MIMEBase
from email.MIMEText import MIMEText
from email.Utils import COMMASPACE, formatdate
from email import Encoders
...
def sendMail(sender_name, to, subject, text, files=None,server="localhost"):
assert type(to)==list
if files:
assert type(files)==list
print "Files: ",files
fro = sender_name
msg = MIMEMultipart()
msg['From'] = fro
msg['To'] = COMMASPACE.join(to)
msg['Date'] = formatdate(localtime=True)
msg['Subject'] = subject
msg.attach( MIMEText(text) )
if files:
for file in files:
# ************** File attaching - Start **************
part = MIMEBase('application', "octet-stream")
part.set_payload( open(file,"rb").read() )
Encoders.encode_base64(part)
part.add_header('Content-Disposition', 'attachment; filename="%s"' % os.path.basename(file))
msg.attach(part)
# ************** File attaching - End **************
server.set_debuglevel(1)
server.ehlo()
server.starttls()
server.ehlo()
server.sendmail(fro, to, msg.as_string())
server.quit()
I get the mail, and the attachments are there, but for some reason, they are
truncated a bit. My guess is I'm missing something in the encoding process.
For example:
Attachment 1: Original file byte count is 1433902, while the new byte count is
1433600
Attachment 2: Original file byte count is 2384703, while the new byte count is
2383872
Any ideas?
Answer: Found the problem. Turns out I tried sending the files before the buffer of
the writing process was fully flushed.
So, it was a synchronization issue and not an encoding issue.
Sorry about that, and thanks for the help guys!
|
Using python datetime.datetime.strptime on windows with BST timezone
Question: I need to parse many different dates in many different formats. I am having
trouble with the following and wondered if anyopne could explain why;
The following works on a linux system:
from datetime import datetime
datetime.strptime('Tue 23 Aug 2011 09:00:07 PM BST','%a %d %b %Y %H:%M:%S %p %Z')
But running under windows it raises
ValueError: time data does not match format
However, if I try GMT not BST on windows, it works fine;
from datetime import datetime
datetime.strptime('Tue 23 Aug 2011 09:00:07 PM GMT','%a %d %b %Y %H:%M:%S %p %Z')
Is there a reason python does not understand the BST timezone under windows,
but it works fine under Linux?
thanks,
Matt.
Answer: In my opinion, parsing a three-letter time zone code like this is not a good
practice (unless of course you have no choice). For example, "EST" is commonly
used in the USA for UTC-4/5 and is also commonly used in Australia. So any
support for "EST" must therefore be dependent on locale. It would not surprise
me if "BST" was similarly ambiguous.
I highly recommend using the [`pytz`](http://pypi.python.org/pypi/pytz/)
module in which British civil time is given the string identifier
`Europe/London` and UTC is called `Etc/UTC`. The `pytz` API will give
consistent results regardless of the locale of the user or system running the
application.
If you are working on a UI that must be tied to locale, or parsing inputs with
formats you cannot change, then consider using a dictionary of abbreviations
to `pytz` timezone objects. For example: `{'BST': 'Europe/London'}`. Then your
application can work with UTC dates and times uniformly, which will greatly
reduce the possibility of errors.
|
Deploying Django app using passenger
Question: I can get through everything on their wiki - and then I'm lost.
<http://wiki.dreamhost.com/Django>
I have a blank Django template, and whenever I try to change anything I get a
500 internal server error.
I have completely developed my django app locally and just want to host it
online - figured it would be easy but am slowly learning that it is not.
I upload my app "videos" to this directory and then put it into the installed
apps and ran "python manage.py syncdb", which finds no fixtures (which I Found
odd).
From there, it just gets an internal server error.
Here is the error I am getting: <http://tweettune.com/> and here is the error
log:
[Wed Aug 24 01:49:15 2011] [error] [client 66.212.30.122] Premature end of script headers:
[Wed Aug 24 01:49:15 2011] [error] [client 66.212.30.122] Premature end of script headers: internal_error.html
[Wed Aug 24 08:16:40 2011] [error] [client 99.229.160.94] Premature end of script headers:
[Wed Aug 24 08:16:41 2011] [error] [client 99.229.160.94] Premature end of script headers: internal_error.html
[Wed Aug 24 08:21:38 2011] [error] [client 99.229.160.94] Premature end of script headers:
[Wed Aug 24 08:21:38 2011] [error] [client 99.229.160.94] Premature end of script headers: internal_error.html
[Wed Aug 24 08:27:41 2011] [error] [client 99.229.160.94] Premature end of script headers:
[Wed Aug 24 08:27:41 2011] [error] [client 99.229.160.94] Premature end of script headers: internal_error.html
I've been trying for 6 hours now and can not figure out what I am doing wrong.
I suppose I just don't understand how to deploy an application at all - my
thought process now is take my locally hosted app and replace all the files in
the default django template online. I don't see why this should not work but
it's not. I tried the "hello world app" example by using this code in my
passenger_wdgi file and it works...
def application(environ, start_response):
start_response('200 OK', [('Content-type', 'text/plain')])
return ["Hello, world!"]
Any direction would be helpful.
**EDIT:** Here are the contents of my passenger_wsgi.py file which may be
helpful (although it is automatically generated by dreamhost...so figured it
would be correct).
import sys, os
sys.path.append(os.getcwd())
os.environ['DJANGO_SETTINGS_MODULE'] = "sotd.settings"
import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()
project_path='/home/tweettune.com/sotd/'
sys.path.insert(1, project_path)
Answer: I had the same problem. The solution was to add the folder of my application
in the wsgi_passenger.py
import sys, os
sys.path.append(os.getcwd())
sys.path.append(os.path.join(os.getcwd(), 'include your apps folder here'))
os.environ['DJANGO_SETTINGS_MODULE'] = "cpc.settings"
import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()
This link was very useful to me:
<http://discussion.dreamhost.com/thread-128918.html>
|
psycopg2.ProgrammingError, running script to serialize data of django app from postgres
Question: I have a `djano web app` which stores the data about some entries to `postgres
db`.To copy the data in db to `json file`s ,I generally use the `python
manage.py shell` and use the serialization api as mentioned i django tutorial.
>>>python manage.py shell
...
In[8]:from myapp.models import MyFirstModel
In[9]:data = serializers.serialize("xml", MyFirstModel.objects.all())
In[10]:print data
I copy this output to some text file and save it as json.
I thought of writing a script to do this and tried
datacopy.py ........
...
filename = os.path.join(dirpath,basefilename+".json")
def write_data_to_file():
from django.core import serializers
XMLSerializer = serializers.get_serializer("json")
xml_serializer = XMLSerializer()
out = open(filename,"a")
from django.contrib.auth.models import User
from myapp.models import MyFirstModel
from myapp.models import MyNextModel
xml_serializer.serialize(User.objects.all(), stream=out)
xml_serializer.serialize(MyFirstModel.objects.all(), stream=out)
xml_serializer.serialize(MyNextModel.objects.all(), stream=out)
if __name__ == '__main__':
write_data_to_file()
From bash shell,I tried
>>python datacopy.py
But, this writes only the User model's data and fails to copy the models which
I create in my app.
The error message I get
Traceback (most recent call last):
File "datacopy.py", line 29, in <module>
write_data_to_file()
File "datacopy.py", line 23, in write_data_to_file
xml_serializer.serialize(MyFirstModel.objects.all(), stream=out)
File "/home/me/Django-1.1.1/django/core/serializers/base.py", line 38, in serialize
for obj in queryset:
File "/home/me/Django-1.1.1/django/db/models/query.py", line 106, in _result_iter
self._fill_cache()
File "/home/me/Django-1.1.1/django/db/models/query.py", line 692, in _fill_cache
self._result_cache.append(self._iter.next())
File "/home/me/Django-1.1.1/django/db/models/query.py", line 238, in iterator
for row in self.query.results_iter():
File "/home/me/Django-1.1.1/django/db/models/sql/query.py", line 287, in results_iter
for rows in self.execute_sql(MULTI):
File "/home/me/Django-1.1.1/django/db/models/sql/query.py", line 2369, in execute_sql
cursor.execute(sql, params)
File "/home/me/Django-1.1.1/django/db/backends/util.py", line 19, in execute
return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: relation "myapp_myfirstmodel" does not exist
I am able to copy data of all three models when I use the `python manage.py
shell`.Why does this error happen when I run the script from bash?I have the
modules of myapp in PYTHONPATH
Answer: Have you looked in to using ./manage.py dumpdata ? You can specify the
serialization format.
For your script to work have you set DJANGO_SETTINGS to the correct
settings.py ?
Secondly is there a reason that you are doing your imports inside the
function, probably better to move them to the head of the file:
from django.core import serializers
from django.contrib.auth.models import User
from myapp.models import MyFirstModel
from myapp.models import MyNextModel
def write_data_to_file():
XMLSerializer = serializers.get_serializer("json")
xml_serializer = XMLSerializer()
out = open(filename,"a")
|
Can modules with a common package hierarchy mentioned multiple times in my PYTHONPATH?
Question: I have two separate projects that share a package name. They run OK as long as
they are not both on the PYTHONPATH, but as soon as they both appear one of
them cannot find imports in its own project.
Example, two projects like this:
Project 1:
x/
__init__.py
test.py
foo.py
test.py contains the line:
import x.foo
Project 2:
x/
__init__.py
bar.py
If I run
PYTHONPATH=. python x/y/test.py
there is no error. But if I run
PYTHONPATH='pathtoproject2:.' python x/test.py
I get the error:
Traceback (most recent call last):
File "x/test.py", line 1, in <module>
import x.foo
ImportError: No module named foo
Is there a way to have different Python projects with a common package share
the PYTHONPATH? Or will Python always use only the first path where a package
is found?
Note: I know if you modify the import from x.foo to import foo then it will
work. But I want to know if it is possible to do it without modifying either
package.
Answer: Currently, Python does not support packages from different directories. A
package is an unit, not just a namespace. This is different from Java
"packages" or the more appropriately named "namespaces" in .NET.
When importing a package, Python will scan `sys.path`, sequentially, and use
the first match. If there is another module or package with a matching name in
a directory that appears later in the path, it won't be found.
Your "note" is not true, by the way. When you use `import foo`, Python will
try a relative import within the directory of `test.py`, find no match, then
attempt an absolute import of module `foo`, which does not exist either, and
then raise an `ImportError`.
Instead of using package names to group modules using a common prefix, think
of packages as smallish, self-contained libraries. In Python, [_flat is better
than nested_](http://www.python.org/dev/peps/pep-0020/), and it is preferable
to have multiple top-level packages, each fulfilling one distinct purpose,
than having one large monolithic package. Instead of `org.example.foo` and
`org.example.bar`, just use `foo` and `bar`.
|
Python dir() not displaying all modules in a package
Question: I'm using python 2.6 and I'm seeing somewhat weird behavior with the `dir()`
function. I'm trying to import all the modules from a directory/package for a
unittest but when I do a `dir()` on on the folder, I don't get _all_ the
modules in that directory.
**Sample directory structure:**
|-mod_dir\
|---__init__.py
|---modA.py
|---modB.py
|---modC.py
|
|-mod_tests\
|---__init__.py
|---test.py
**Sample test.py:**
import mod_dir
for obj in dir(mod_dir):
print obj
Unfortunately, at this point I only get something like:
modA
__all__
__builtins__
__doc__
__file__
__name__
__package__
__path__
Any ideas as to why the others aren't appearing here? I don't think it
matters, but the `__init__.py` file in the mod_dir is empty. I've tried
setting the `__all__` variable but it has no effect. If it does matter,
however, I'm using this in WinXp with pydev in eclipse.
**Context:**
Each module under mod_dir has a unittest in it and I'm trying to include them
in a unittest suite within test.py. I'm aware of nose and other methods like
[this](http://stackoverflow.com/questions/555571/getting-a-list-of-all-
modules-in-the-current-package/555717#555717) one, but I'm more interested in
why dir isn't displaying everything.
Answer: I believe it does matter that the `__init__.py` file is empty.
Try this in the `__init__.py`:
import modA
import modB
import modC
From the python docs, [`dir` should not be used for
this](http://docs.python.org/library/functions.html#dir) (see the Note at the
bottom of the `dir` section). It's not rigorous enough, and mainly used in the
interactive prompt.
|
speeding up numpy kronecker products
Question: I am working on my first large python project. I have one function which has
the following code in it:
# EXPAND THE EXPECTED VALUE TO APPLY TO ALL STATES,
# THEN UPDATE fullFnMat
EV_subset_expand = np.kron(EV_subset, np.ones((nrows, 1)))
fullFnMat[key] = staticMat[key] + EV_subset_expand
In my code profiler, it seems like this kronecker product is actually taking
up a huge amount of time.
Function was called by...
ncalls tottime cumtime
/home/stevejb/myhg/dpsolve/ootest/tests/ddw2011/profile_dir/BellmanEquation.py:17(bellmanFn) <- 19 37.681 38.768 /home/stevejb/myhg/dpsolve/ootest/tests/ddw2011/profile_dir/dpclient.py:467(solveTheModel)
{numpy.core.multiarray.concatenate} <- 342 27.319 27.319 /usr/lib/pymodules/python2.7/numpy/lib/shape_base.py:665(kron)
/home/stevejb/myhg/dpsolve/ootest/tests/ddw2011/profile_dir/dpclient.py:467(solveTheModel) <- 1 11.041 91.781 <string>:1(<module>)
{method 'argsort' of 'numpy.ndarray' objects} <- 19 7.692 7.692 /usr/lib/pymodules/python2.7/numpy/core/fromnumeric.py:597(argsort)
/usr/lib/pymodules/python2.7/numpy/core/numeric.py:789(outer) <- 171 2.526 2.527 /usr/lib/pymodules/python2.7/numpy/lib/shape_base.py:665(kron)
{method 'max' of 'numpy.ndarray' objects} <- 209 2.034 2.034 /home/stevejb/myhg/dpsolve/ootest/tests/ddw2011/profile_dir/dpclient.py:391(getValPolMatrices)
Is there a way to get faster kronecker products in Numpy? It seems like it
shouldn't take as long as it is.
Answer: You can certainly take a look at the source for `np.kron`. It can be found in
`numpy/lib/shape_base.py`, and you can see if there are improvements that can
be made or simplifications that might make it more efficient. Alternatively
you could write your own using Cython or some other binding to a low level
language to try to eek out better performance.
Or as @matt suggested something like the following might be natively faster:
import numpy as np
nrows = 10
a = np.arange(100).reshape(10,10)
b = np.tile(a,nrows).reshape(nrows*a.shape[0],-1) # equiv to np.kron(a,np.ones((nrows,1)))
or:
b = np.repeat(a,nrows*np.ones(a.shape[0],np.int),axis=0)
Timings:
In [80]: %timeit np.tile(a,nrows).reshape(nrows*a.shape[0],-1)
10000 loops, best of 3: 25.5 us per loop
In [81]: %timeit np.kron(a,np.ones((nrows,1)))
10000 loops, best of 3: 117 us per loop
In [91]: %timeit np.repeat(a,nrows*np.ones(a.shape[0],np.int),0)
100000 loops, best of 3: 12.8 us per loop
Using `np.repeat` for the sized arrays in the above example gives a pretty
nice 10x speed-up, which isn't too shabby.
|
In Python App Engine How Do I Uniquely Identify An Instance Of My App Running On The Dev SDK?
Question: My application relies on an external service that it communicates with using
urlfetch. I have multiple developers each running their own instance of my
application on their development computers while they add features. Each
developer instance needs to be able to uniquely identify itself to the
external service so that the external service can keep their data separated.
I need a way to automatically generate a unique identifier for each developer
from within the application.
Yes, I could just have each developer put a unique id in a variable in their
code but I would much prefer it was automatic.
Also, I could probably read some information about the hardware on the
computer (like MAC address) and use that but I want this code to use only
things that work on the production server so that I can use it there
eventually as well.
Answer: The only trick I've seen to identify instances is using a global variable
address.
UNIQUE_INSTANCE_ID = {} # at module level
logging.debug("Instance %s." % (str("%X" % id( UNIQUE_INSTANCE_ID )).zfill(16)))
That seems to work fairly well to uniquely identify an instance; but it only
identifies an instance, not a machine. So if you restart your instance, you
get a new identifier. That might be a "feature".
You could also use some of the META variables; if developers are all running
out of a home directory, you could parse a username out of 'PATH_TRANSLATED'.
At the very least, you could make injecting a UUID into the datastore part of
the data population; store a metadata kind in the datastore and the cache, and
wrap that UUID into the requests.
from uuid import uuid4
from google.appengine.ext import db
from google.appengine.api import memcache
cache = memcache.Client()
class InstanceStamp(db.Model):
code = db.StringProperty()
INSTANCE_STAMP_KEY = "instance_stamp"
@classmethod
def get_stamp(cls):
cache_key = cls.INSTANCE_STAMP_KEY
stamp_code = cache.get(cache_key)
if stamp_code is None:
code = uuid4().hex
stamp = cls.get_or_insert('instance_stamp', code=code)
if stamp is not None:
cache.set(cache_key, stamp.code, 300)
stamp_code = stamp.code
return stamp_code
|
hasattr(obj, '__iter__') vs collections
Question: I've seen a couple posts recommending `isinstance(obj, collections.Sequence)`
instead of `hasattr(obj, '__iter__')` to determine if something is a list.
[len(object) or hasattr(object,
__iter__)?](http://stackoverflow.com/questions/1763507/lenobject-or-
hasattrobject-iter)
[Python: is not sequence](http://stackoverflow.com/questions/2937114/python-
is-not-sequence)
At first I was excited because testing if an object has `__iter__` always
seemed dirty to me. But after further review this still seems to be the best
solution because none of the `isinstance` tests on `collection` yield the same
results. `collections.Sequence` is close but it returns `True` for strings.
hasattr(obj, '__iter__')
set([]): True
{}: True
[]: True
'str': False
1: False
isinstance(obj, collections.Iterable)
set([]): True
{}: True
[]: True
'str': True
1: False
isinstance(obj, collections.Iterator)
set([]): False
{}: False
[]: False
'str': False
1: False
isinstance(obj, collections.Sequence)
set([]): False
{}: False
[]: True
'str': True
1: False
Here is the code I used to generate this:
import collections
testObjs = [
set(),
dict(),
list(),
'str',
1
]
print "hasattr(obj, '__iter__')"
for obj in testObjs:
print ' %r: %r' % (obj, hasattr(obj, '__iter__'))
print
print "isinstance(obj, collections.Iterable)"
for obj in testObjs:
print ' %r: %r' % (obj, isinstance(obj, collections.Iterable))
print
print "isinstance(obj, collections.Iterator)"
for obj in testObjs:
print ' %r: %r' % (obj, isinstance(obj, collections.Iterator))
print
print "isinstance(obj, collections.Sequence)"
for obj in testObjs:
print ' %r: %r' % (obj, isinstance(obj, collections.Sequence))
print
Am I missing something or is `hasattr(obj, '__iter__')` still the best option
for testing if something is iterable?
**EDIT:** I am only interested in detecting the builtin types: `dict`, `list`,
and `set`.(**EDIT:** this is foolish :))
**EDIT:** I should have included the use case that got me looking into this. I
have a function that takes an arg that can be a single value or a sequence. So
I want to detect what it is and turn it into a sequence if it's a single value
so I can deal with it as a sequence after that.
if hasattr(arg, '__iter__'):
arg= set(arg)
else:
arg= set([arg])
One solution to this is just to let it throw an exception if the object cannot
be iterated. But that doesn't work in my use case. Another solution is to use
something like:
import collections
def issequenceforme(obj):
if isinstance(obj, basestring):
return False
return isinstance(obj, collections.Sequence)
_From:_ [Python: is not
sequence](http://stackoverflow.com/questions/2937114/python-is-not-sequence)
But this requires this function to be defined which makes me not want to use
it.
It looks like `hasattr(arg, '__iter__')` is still the best option.
Answer: The `collections.Iterable` will guarantee the object is iterable or not (like
using `for x in obj`) but checking `__iter__` will not.
A string is a iterable datatype but on Python2.x it doesn't have a `__iter__`
method.
|
I don't even know what infile > outfile means. How am I supposed to use it?
Question: I don't know how to use Python, and I'm trying to use a script on a document.
I have no idea how to tell it do this!
If I just run the script, this is the message I get:
Use: C:\Python27\hun2html.py infile > outfile
Traceback (most recent call last):
File "C:\Python27\hun2html.py", line 75, in <module>
sys.exit(1)
SystemExit: 1
I'm not sure what info is relevant to anyone who knows about this stuff, but
this is the most relevant part of the code, I believe:
if __name__ == '__main__':
import sys
if not sys.argv[1:]:
print "Use: %s infile > outfile" % sys.argv[0]
sys.exit(1)
contents = open(sys.argv[1]).read()
print hun2html(contents)
It's supposed to change the formatting in a document. If anyone can make sense
of this stupid question, I would really appreciate some help!
Answer: It means that you should write the path to the file you want to use for input
where infile is and the path to the file you want to store the output where
outfile is. For example,
C:\Python27\hun2html.py C:\input.txt > C:\output.txt
Note that the input file is being passed as a parameter (accessed in the code
by `sys.argv[1]` ) and the output is being piped, meaning that the Python
prints it to standard output, but because you put the `>` character it will be
redirected to the file you indicate. If you left off the `> outfile` you would
see the output displayed on your terminal.
|
Python URL variable int add to string
Question:
pgno = 1
while pgno < 4304:
result = urllib.urlopen("http://www.example.comtraderesourcespincode.aspx?" +
"&GridInfo=Pincode0"+ pgno)
print pgno
html = result.read()
parser = etree.HTMLParser()
tree = etree.parse(StringIO.StringIO(html), parser)
pgno += 1
in `http://.......=Pincode0` I need to add 1..for e.g like 'Pincode01', loop
it 01 to 02, 03 .. for which I am using a while loop and the variable assigned
is 'pgno'.
The problem is the counter is adding 1, but 'Pincode01' is not becoming
'Pincode02' ... therefore it is not opening the 2nd page of the site.
I even tried `+str(pgno))` ... no luck.
Please show how to do it. I am not able to do this ...and have attempted it
several times.
Answer: Probably, you want this :
from urllib import urlopen
import re
pgno = 2
url = "http://www.eximguru.com/traderesources/pincode.aspx?&GridInfo=Pincode0%s" %str(pgno)
print url +'\n'
sock = urlopen(url)
htmlcode = sock.read()
sock.close()
x = re.search('%;"><a href="javascript:__doPostBack',htmlcode).start()
pat = ('\t\t\t\t<td style="width:\d+%;">(\d+)</td>'
'<td style="width:\d+%;">(.+?)</td>'
'<td style="width:\d+%;">(.+?)</td>'
'<td style="width:30%;">(.+?)</td>\r\n')
regx = re.compile(pat)
print '\n'.join(map(repr,regx.findall(htmlcode,x)))
result
http://www.eximguru.com/traderesources/pincode.aspx?&GridInfo=Pincode02
('110001', 'New Delhi', 'Delhi', 'Baroda House')
('110001', 'New Delhi', 'Delhi', 'Bengali Market')
('110001', 'New Delhi', 'Delhi', 'Bhagat Singh Market')
('110001', 'New Delhi', 'Delhi', 'Connaught Place')
('110001', 'New Delhi', 'Delhi', 'Constitution House')
('110001', 'New Delhi', 'Delhi', 'Election Commission')
('110001', 'New Delhi', 'Delhi', 'Janpath')
('110001', 'New Delhi', 'Delhi', 'Krishi Bhawan')
('110001', 'New Delhi', 'Delhi', 'Lady Harding Medical College')
('110001', 'New Delhi', 'Delhi', 'New Delhi Gpo')
('110001', 'New Delhi', 'Delhi', 'New Delhi Ho')
('110001', 'New Delhi', 'Delhi', 'North Avenue')
('110001', 'New Delhi', 'Delhi', 'Parliament House')
('110001', 'New Delhi', 'Delhi', 'Patiala House')
('110001', 'New Delhi', 'Delhi', 'Pragati Maidan')
('110001', 'New Delhi', 'Delhi', 'Rail Bhawan')
('110001', 'New Delhi', 'Delhi', 'Sansad Marg Hpo')
('110001', 'New Delhi', 'Delhi', 'Sansadiya Soudh')
('110001', 'New Delhi', 'Delhi', 'Secretariat North')
('110001', 'New Delhi', 'Delhi', 'Shastri Bhawan')
('110001', 'New Delhi', 'Delhi', 'Supreme Court')
('110002', 'New Delhi', 'Delhi', 'Rajghat Power House')
('110002', 'New Delhi', 'Delhi', 'Minto Road')
('110002', 'New Delhi', 'Delhi', 'Indraprastha Hpo')
('110002', 'New Delhi', 'Delhi', 'Darya Ganj')
I wrote this code after having studied the structure of the HTML source code
with the following code (I think you'll understand it without any more
explanations):
from urllib2 import Request,urlopen
import re
pgno = 2
url = "http://www.eximguru.com/traderesources/pincode.aspx?&GridInfo=Pincode0%s" %str(pgno)
print url +'\n'
sock = urlopen(url)
htmlcode = sock.read()
sock.close()
li = htmlcode.splitlines(True)
print '\n'.join(str(i) + ' ' + repr(line)+'\n' for i,line in enumerate(li) if 275<i<300)
ch = ''.join(li[0:291])
from collections import defaultdict
didi =defaultdict(int)
for c in ch:
didi[c] += 1
print '\n\n'+repr(li[289])
print '\n'.join('%r -> %s' % (c,didi[c]) for c in li[289] if didi[c]<35)
.
Now, the problem is that the same HTML is returned for all the values of pgno.
The site may detect it is a program that wants to connect and fetch data. This
problem must be treated with the tools in **urllib2** , but I'm not trained to
that.
|
Python create/import custom module in same directory
Question: I'm trying to create a simple python script and import a couple of custom
classes. I'd like to do this as one module. Here is what I have:
point/point.py
class Point:
"""etc."""
point/pointlist.py
class PointList:
"""etc."""
point/__init__.py
from . import point, pointlist
script.py
import sys, point
verbose = False
pointlist = PointList()
When I run `script.py` I get `NameError: name 'PointList' is not defined`
What's weird is that in point/, all three of the module files (__init__,
pointlist, point) have a `.pyc` version created that was not there before, so
it seems like it is finding the files. The class files themselves also compile
without any errors.
I feel like I'm probably missing something very simple, so please bear with
me.
Answer: Sorry, I seem to have made a blunder in my earlier answer and comments:
The problem here is that you should access the objects in `point` through the
module you import:
`point/__init__.py`:
from point import Point
from pointlist import PointList
`script.py:`
import sys, point
verbose = False
pointlist = point.PointList()
You access `PointList` through the import `point` which imports whatever is in
`__init__.py`
If you want to access `PointList` and `Point` directly you could use `from
point import Point, PointList` in `script.py` or the least preferable `from
point import *`
Again, sorry for my earlier error.
|
How to generate a Cocoa-recognized plot using matplotlib in Python on OS X (Leopard preferably)
Question: I'm not sure exactly what is going on under the hood, but here is my setup,
example code, and problem:
## setup:
* snow leopard (10.6.8)
* Python 2.7.2 (provide by EPD 7.1-2)
* iPython 0.11 (provided by EPD 7.1-2)
* matplotlib (provided by EPD 7.1-2)
## example code:
import numpy as np
import pylab as pl
x=np.random.normal(size=(1000,))
pl.plot(x)
## problem:
I can't use the standard Mac OS X shorcuts to access the window generated by
the plot command.
For example, I can't `Command`-`Tab` to the window. Thus, if the window is
behind some other window, I need to _mouse_ over to it! `Command`-`W` doesn't
close it.
Obviously, this is unacceptable. It seems like perhaps running Lion instead of
Leopard might fix this, but i haven't upgraded yet. I feel like the problem
has something to do with iPython generating windows that aren't fully Cocoa-
aware in some sense, but I really know very little so I'm not particularly
confident in this hypothesis.
Thus, any ideas on how to either resolve or get around this issue would be
much appreciated.
Answer: From the description on the [iPython page](http://ipython.org/), it looks like
Python uses **Qt** to generate UI. This means that the windows it generates
are definitely not Cocoa windows and will not act like them.
There's not likely to be an easy solution to this issue.
|
Caught DatabaseError while rendering: no such column: bookmarks_bookmark.title
Question: Learning django from "learning website development using django". In chapter
3, building a bookmark data model, I followed the instructions and code given
except for--
from django.contrib.auth.models import User
class Bookmark(models.Model):
title = models.CharField(maxlength=200)
user = models.ForeignKey(User)
link = models.ForeignKey(Link)
where I changed
title = models.CharField(maxlength=200)
into
title = models.CharField(max_length=200)
as I was geting an error message. After that, I ran python manage.py syncdb,
then, python manage.py sql bookmarks. When I checked
<http://localhost:8000/user/my_username>, I get this error message:
Request Method: GET
Request URL: http://127.0.0.1:8000/user/j/
Django Version: 1.3
Exception Type: TemplateSyntaxError
Exception Value:
**Caught DatabaseError while rendering: no such column: bookmarks_bookmark.title**
Looking this up, I learned that sqlite3, the database i was using, cannot find
bookmarks_bookmark.title. I went back into the book to make sure I have
everything copied correctly, and I did except for that part that I changed
(max_length). When I ran python manage.py sql bookmarks, it gave me--
BEGIN;
CREATE TABLE "bookmarks_bookmark" (
"id" integer NOT NULL PRIMARY KEY,
"title" varchar(200) NOT NULL,
"user_id" integer NOT NULL REFERENCES
"auth_user" ("id"),
"link_id" integer NOT NULL REFERENCES
"bookmarks_link" ("id"),
);
CREATE TABLE "bookmarks_link" (
"id" integer NOT NULL PRIMARY KEY,
"url" varchar(200) NOT NULL UNIQUE
);
COMMIT;
How do I fix this? Thanks!
Answer: Manual deleting works.
sqlite3 yourdb.db
> drop table bookmarks_bookmark;
> .quit
cd yourpythonproj
python2 manage.py syncdb
python2 manage.py runserver
bash script
#!/bin/bash
sqlite3 ../yourdb.db 'drop table yourtable'
python2 manage.py syncdb
|
parallel recursive function in python?
Question: How do I parallelize a recursive function in Python?
My function looks like this:
def f(x, depth):
if x==0:
return ...
else :
return [x] + map(lambda x:f(x, depth-1), list_of_values(x))
def list_of_values(x):
# heavy compute, pure function
When trying to parallelize it with `multiprocessing.Pool.map`, windows opens
infinite number of processes and hangs.
What's a good (preferably simple) way to parallelize it (for a single
multicore machine) ?
Here is the code that hangs:
from multiprocessing import Pool
pool = pool(processes=4)
def f(x, depth):
if x==0:
return ...
else :
return [x] + pool.map(lambda x:f(x, depth-1), list_of_values(x))
def list_of_values(x):
# heavy compute, pure function
Answer: ok, sorry for the problems with this.
i'm going to answer a slightly different question where `f()` returns the sum
of the values in the list. that is because it's not clear to me from your
example what the return type of `f()` would be, and using an integer makes the
code simple to understand.
this is complex because there are two different things happening in parallel:
1. the calculation of the expensive function in the pool
2. the recursive expansion of `f()`
i am very careful to only use the pool to calculate the expensive function. in
that way we don't get an "explosion" of processes. but because this is
asynchronous we need to postpone a _lot_ of work for the callback that the
worker calls once the expensive function is done.
more than that, we need to use a countdown latch so that we know when all the
separate sub-calls to `f()` are complete.
there may be a simpler way (i am pretty sure there is, but i need to do other
things), but perhaps this gives you an idea of what is possible:
from multiprocessing import Pool, Value, RawArray, RLock
from time import sleep
class Latch:
'''A countdown latch that lets us wait for a job of "n" parts'''
def __init__(self, n):
self.__counter = Value('i', n)
self.__lock = RLock()
def decrement(self):
with self.__lock:
self.__counter.value -= 1
print('dec', self.read())
return self.read() == 0
def read(self):
with self.__lock:
return self.__counter.value
def join(self):
while self.read():
sleep(1)
def list_of_values(x):
'''An expensive function'''
print(x, ': thinking...')
sleep(1)
print(x, ': thought')
return list(range(x))
pool = Pool()
def async_f(x, on_complete=None):
'''Return the sum of the values in the expensive list'''
if x == 0:
on_complete(0) # no list, return 0
else:
n = x # need to know size of result beforehand
latch = Latch(n) # wait for n entires to be calculated
result = RawArray('i', n+1) # where we will assemble the map
def delayed_map(values):
'''This is the callback for the pool async process - it runs
in a separate thread within this process once the
expensive list has been calculated and orchestrates the
mapping of f over the result.'''
result[0] = x # first value in list is x
for (v, i) in enumerate(values):
def callback(fx, i=i):
'''This is the callback passed to f() and is called when
the function completes. If it is the last of all the
calls in the map then it calls on_complete() (ie another
instance of this function) for the calling f().'''
result[i+1] = fx
if latch.decrement(): # have completed list
# at this point result contains [x]+map(f, ...)
on_complete(sum(result)) # so return sum
async_f(v, callback)
# Ask worker to generate list then call delayed_map
pool.apply_async(list_of_values, [x], callback=delayed_map)
def run():
'''Tie into the same mechanism as above, for the final value.'''
result = Value('i')
latch = Latch(1)
def final_callback(value):
result.value = value
latch.decrement()
async_f(6, final_callback)
latch.join() # wait for everything to complete
return result.value
print(run())
ps i am using python3.2 and the ugliness above is because we are delaying
computation of the final results (going back up the tree) until later. it's
possible something like generators or futures could simplify things.
also, i suspect you need a cache to avoid needlessly recalculating the
expensive function when called with the same argument as earlier.
see also yaniv's answer - [parallel recursive function in
python?](http://stackoverflow.com/questions/7222570/parallell-recursive-
function-in-python/7228414#7228414) \- which seems to be an alternative way to
reverse the order of the evaluation by being explicit about depth.
|
Running pdb in daemon mode with WSGI
Question: I am running a Python script on Apache 2.2 with mod wsgi.
Is it possible to run pdb.set_trace() in a python script using daemon mode in
wsgi?
**Edit** The reason I want to use daemon mode instead of embedded mode is to
have the capability to reload code without having to restart the Apache server
every time (which embedded mode requires). I would like to be able to use code
reloading without restarting Apache everytime and still be able to use pdb...
Answer: I had the same need to be able to use the amazingly powerful `pdb`, dropping a
`pdb.set_trace()` wherever I wanted to debug some part of the Python server
code.
Yes, **Apache** spawns the **WSGI** application in a place where it is out of
your control [1]. But I found a good compromise is to
1. maintain your Apache `WSGIScriptAlias`
2. and also give yourself the option of starting your Python server in a terminal as well (testing locally and not through **Apache** anymore in this case)
So if one uses `WSGIScriptAlias` somewhat like this... pointing to your python
WSGI script called `webserver.py`
<VirtualHost *:443>
ServerName myawesomeserver
DocumentRoot /opt/local/apache2/htdocs
<Directory /opt/local/apache2/htdocs>
[...]
</Directory>
WSGIScriptAlias /myapp /opt/local/apache2/my_wsgi_scripts/webserver.py/
<Directory /opt/local/apache2/my_wsgi_scripts/>
[...]
</Directory>
[...]
SSLEngine on
[...]
</VirtualHost>
And so your `webserver.py` can have a simple **switch** to go between being
used by Apache and getting started up for debugging manually.
Keep a flag in your config file such as, in some `settings.py`:
WEBPY_WSGI_IS_ON = True
And `webserver.py` :
import web
import settings
urls = (
'/', 'excellentWebClass',
'/store', 'evenClassier',)
if settings.WEBPY_WSGI_IS_ON is True:
# MODE #1: Non-interactive web.py ; using WSGI
# So whenever true, the Web.py application here will talk wsgi.
application = web.application(urls, globals()).wsgifunc()
class excellentWebClass:
def GET(self, name):
# Drop a pdb wherever you want only if running manually from terminal.
pdb.set_trace()
try:
f = open (name)
return f.read()
except IOError:
print 'Error: No such file %s' % name
if __name__ == "__main__":
# MODE #2: Interactive web.py , for debugging.
# Here you call it directly.
app = web.application(urls, globals())
app.run()
So when you want to test out your webserver interactively, you just run it
from a terminal,
$ python webserver.py 8080
starting web...
http://0.0.0.0:8080/
_[1] Footnote: There are some really complex ways of getting Apache child
processes under your control, but I think the above is much simpler if you
just want to debug your Python server code. And if there are actually easy
ways, then I would love to learn about those too._
|
Invalid Python syntax using file.write
Question: Trying to learn some geospatial python. More or less following the class notes
[here](http://www.gis.usu.edu/~chrisg/python/2009/lectures/ospy_slides1.pdf).
[My Code](http://pastebin.com/pp2b0CvF)
#!/usr/bin/python
# import modules
import ogr, sys, os
# set working dir
os.chdir('/home/jacques/misc/pythongis/data')
# create the text file we're writing to
file = open('data_export.txt', 'w')
# import the required driver for .shp
driver = ogr.GetDriverByName('ESRI Shapefile')
# open the datasource
data = driver.Open('road_surveys.shp', 1)
if data is None:
print 'Error, could not locate file'
sys.exit(1)
# grab the datalayer
layer = data.GetLayer()
# loop through the features
feature = layer.GetNextFeature()
while feature:
# acquire attributes
id = feature.GetFieldAsString('Site_Id')
date = feature.GetFieldAsString('Date')
# get coordinates
geometry = feature.GetGeometryRef()
x = str(geometry.GetX())
y = str(geometry.GetY()
# write to the file
file.Write(id + ' ' + x + ' ' + y + ' ' + cover + '\n')
# remove the current feature, and get a new one
feature.Destroy()
feature = layer.GetNextFeature()
# close the data source
datasource.Destroy()
file.close()
Running that gives me the following:
File "shape_summary.py", line 38
file.write(id + ' ' + x + ' ' + y + ' ' + cover + '\n')
^
SyntaxError: invalid syntax
Running Python 2.7.1
Any help would be fantastic!
Answer: Previous line is missing a close parenthesis:
y = str(geometry.GetY())
Also, just a style comment: it's a good idea to avoid using the variable name
`file` in python because it actually has a meaning. Try opening a new python
session and running `help(file)`
|
Getting Beaker working with GAE
Question: I'm trying to port an app I've been running locally to GAE. The app uses the
Bottle.py framework. I use Beaker for session management. I'm a bit of a noob
and am having trouble getting Beaker imported properly. Help greatly
appreciated.
I'm running the ported app using GoogleAppEngineLauncher.app under Mac OS X
10.6.7. This runs the app in the simulation environment on my machine, not on
Google's servers.
For my GAE port, I've put Bottle.py into a directory called 'framework'. This
directory has an empty `__init__.py` file. Bottle is working fine and can
serve 'hello world'.
Beaker exists in its own directory in the root of my app (journal/beaker).
Beaker also has an empty `__init__.py`.
Relevant code:
from framework import bottle
from beaker import SessionMiddleware
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app
@bottle.route('/')
def index():
return "hello, world"
def main():
bottle.debug(True)
run_wsgi_app(bottle.default_app())
if __name__ == '__main__':
main()
I get an error message like this:
File "/Users/mscantland/code/journal/main.py", line 19, in <module>
from beaker import SessionMiddleware
ImportError: cannot import name SessionMiddleware
Here is what I have tried to get this working so far:
* Checked permissions on everything in /beaker to make sure they were executable.
* Ran beaker as-is and also re-wrote all import statements so that:
from beaker.x import y
became:
from x import y
* Added 'pkg_resources.py' which is not in the standard library for the Python version GAE uses.
Answer: SessionMiddleware is in middleware.py. Try:
from beaker.middleware import SessionMiddleware
|
Django management task won't work on CentOS in crontab or outside project directory
Question: On my local machine (Mac OSX 10.6) I wrote a django custom admin command which
works great. I can use it both within and outside my project directory just
fine. For some reason on my CentOS 5.6 server, it won't work from outside the
project directory. This is really annoying since using this custom admin
command in a cron job requires it to run from the home directory.
in short:
When I run "python ./manage.py scrape" or "python manage.py scrape",
everything is fine.
When I run "python /home/[username]/webapps/myproject/manage.py scrape" or
"python myproject/manage.py scrape", I get the following error:
> unknown command: 'scrape'
>
> Type 'manage.py help' for usage.
On CentOS, when I run manage.py help inside the project directory, scrape
shows up as a command; but if I run it outside the project directory, scrape
does not appear as a valid command. On OS-X scrape appears as a valid command
regardless of where I run manage.py help from.
Any idea how I can fix this?
Answer: I know CentOS ships with Python 2.4, so is your code running on 2.4 or are you
using a contained environment, this is usually fixed by adding your PYTHONPATH
correctly
import sys
print sys.path
verify such for starters
|
Python List: Is this the best way to remove duplicates while preserving order?
Question: > **Possible Duplicates:**
> [How do you remove duplicates from a list in Python whilst preserving
> order?](http://stackoverflow.com/questions/480214/how-do-you-remove-
> duplicates-from-a-list-in-python-whilst-preserving-order)
> [Algorithm - How to delete duplicate elements in a list
> efficiently?](http://stackoverflow.com/questions/1801459/algorithm-how-to-
> delete-duplicate-elements-in-a-list-efficiently)
I've read a lot of methods for removing duplicates from a python list while
preserving the order. All the methods appear to require the creation of a
function/sub-routine, which I think is not very computationally efficient. I
came up with the following and I would like to know if this is the most
computationally efficient method to do so? (My usage for this has to be the
most efficient possible due to the need to have fast response time.) Thanks
b=[x for i,x in enumerate(a) if i==a.index(x)]
Answer: `a.index(x)` itself will be `O(n)` as the list has to be searched for the
value `x`. The overall runtime is `O(n^2)`.
"Saving" function calls does not make a bad algorithm faster than a good one.
More efficient (`O(n)`) would probably be:
result = []
seen = set()
for i in a:
if i not in seen:
result.append(i)
seen.add(i)
Have a look at this question: [How do you remove duplicates from a list in
Python whilst preserving
order?](http://stackoverflow.com/questions/480214/how-do-you-remove-
duplicates-from-a-list-in-python-whilst-preserving-order)
_(the top answer also shows how to do this in a list comprehension manner,
which will be more efficient than an explicit loop)_
* * *
You can easily profile your code yourself using the [`timeit`
_[docs]_](http://docs.python.org/library/timeit.html) module. For example, I
put your code in `func1` and mine in `func2`. If I repeat this `1000` times
with an array with `1000` elements (no duplicates):
>>> a = range(1000)
>>> timeit.timeit('func1(a)', 'from __main__ import func1, a', number=1000)
11.691882133483887
>>> timeit.timeit('func2(a)', 'from __main__ import func2, a', number=1000)
0.3130321502685547
Now with duplicates (only 100 distinct values):
>>> a = [random.randint(0, 99) for _ in range(1000)]
>>> timeit.timeit('func1(a)', 'from __main__ import func1, a', number=1000)
2.5020430088043213
>>> timeit.timeit('func2(a)', 'from __main__ import func2, a', number=1000)
0.08332705497741699
|
Total Python Noob: why doesn't this work?
Question: I'm working through Learn Python the Hard Way, and trying to _understand_ it
rather than just hammer away. I got stuck on Exercise 16, as discussed already
on SO here:
[Very basic Python question (strings, formats and
escapes)](http://stackoverflow.com/questions/6394170/very-basic-python-
question-strings-formats-and-escapes)
but I'm still trying to figure out why this approach does not work:
from sys import argv
script, filename = argv
print "Attempting to open the file now."
print open(filename).read()
print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C."
print "If you do want that, hit RETURN."
raw_input("?")
print "Opening the file..."
target = open(filename, 'w')
print "Truncating the file. Goodbye!"
target.truncate()
print "Now I'm going to ask you for three lines."
line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")
print "I'm going to write these to the file."
linebreak = "\n"
target.write("%s %s %s %s %s %s") % (line1, linebreak, line2, linebreak, line3, linebreak)
target.write("the ending line")
print "And finally, we close it."
target.close()
I've established a value for linebreak, and am calling the line1, line2 and
linebreak values with %s in the target.write command. Should't it parse as
"line1 \n line2 \n line3 \n" when it's read?
This is probably the equivalent of being asked by a child what keeps the sky
up or something, and I apologize for being kind of thick. Thanks!
Answer:
target.write("%s %s %s %s %s %s") % (line1, linebreak, line2, linebreak, line3, linebreak)
should be
target.write("%s %s %s %s %s %s" % (line1, linebreak, line2, linebreak, line3, linebreak))
but would be better written as:
target.write(' '.join(line1, linebreak, line2, linebreak, line3, linebreak))
|
csh stdin to Python stdin?
Question: How do you redirect the stdin of a csh script to the stdin of a python script?
I have a cgi script I'm writing in csh that runs on a Solaris machine. This
csh script is a wrapper to a python script that reads from the stdin (I know,
scripting in csh is bad but I'm forced to in this case).
Thanks for help! (And sorry for the n00b question!)
Answer: test.csh
#!/bin/env csh
python test.py
test.py (see [this question](http://stackoverflow.com/questions/1450393/how-
do-you-read-from-stdin-in-python))
#!/bin/env python
import fileinput
if __name__ == '__main__':
print "Hi. printing stdin"
for line in fileinput.input():
print line
print "fin"
Then the stdin to `test.csh` is passed in to `test.py` [as Henning
said](http://stackoverflow.com/questions/7234640/csh-stdin-to-python-
stdin/7234676#7234676).
echo "this is stdin" | csh test.csh
|
HTTPS to HTTP using CherryPy
Question: Is it possible for CherryPy to redirect HTTP to HTTPS. Lets for example say
the code below is <http://example.com> if someone visits via
<https://example.com> I want them to be redirected to the plain HTTP URL (301
redirect maybe?) how do I accomplish this?
#!/usr/bin/env python
from pprint import pformat
from cherrypy import wsgiserver
def app(environ, start_response):
status = '200 OK'
response_headers = [('Content-type', 'text/plain')]
start_response(status, response_headers)
return [pformat(environ)]
server = wsgiserver.CherryPyWSGIServer(('0.0.0.0', 80), app)
try:
server.start()
except KeyboardInterrupt:
server.stop()
Answer: You can check the `request.scheme` if it is "https" then you can raise a
redirect.
See
<http://docs.cherrypy.org/en/latest/refman/_cprequest.html?highlight=request.scheme#cherrypy._cprequest.Request.scheme>
|
Scaling embedded matplotlib widget in qt application written in python problem
Question: I am writing a simple digital image processing program. To do this I have
embedded a mpl widget in my qt application. The user can perform some simple
analysis on the image such as box car filter, FFT etc. Every thing is working
fine until I would like to switch from displaying an image to displaying a
plot.
If I display a plot first, the axis are fine (see bottom plot in image). But
if I display an image first, followed by a plot (top plot in image), the scale
compresses.
<https://picasaweb.google.com/105163945296073520628/Temp> <\-- sorry I can't
post images yet
The code is hosted here <https://code.launchpad.net/~marrabld/pymi/trunk>
I am using imshow() to display the image. and plot(x,y) for the plots.
This is the main update method
def updateImage(self):
self.ui.mplWidget.canvas.PlotTitle = self.plotTitle
self.ui.mplWidget.canvas.xtitle = self.xTitle
self.ui.mplWidget.canvas.ytitle = self.yTitle
#self.ui.mplWidget.canvas.ax.visible(False)
self.ui.mplWidget.canvas.format_labels()
if self.projectProperty == globals.IMAGE:
if self.lastProjectProperty == globals.PLOT:
self.myImage = imageFuncs.basic(self.imageFileName)
self.imPlot = self.ui.mplWidget.canvas.ax.imshow(self.myImage.image,cmap=matplotlib.cm.gray,origin='upper')
elif self.projectProperty == globals.PLOT:
if self.lastProjectProperty == globals.IMAGE: # we need to reload the GUI
self.ui.mplWidget.canvas.ax.hold(False)
self.ui.mplWidget.canvas.ax.plot(self.xData,self.yData)
self.ui.mplWidget.canvas.draw()
And the mpl widget I am using
#!/usr/bin/env python
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
#from matplotlib.backends.backend_qt4 import NavigationToolbar2QT as NavigationToolbar
from matplotlib.backend_bases import NavigationToolbar2
from matplotlib.figure import Figure
from matplotlib import rc
import numpy as N
class MyMplCanvas(FigureCanvas):
def __init__(self, parent=None, width = 10, height = 12, dpi = 125, sharex = None, sharey = None):
rc('text', usetex=True)
rc('font', family='sans-serif')
rc('legend',fontsize='small' )
rc('legend',shadow='true')
self.fig = Figure(figsize = (width, height), dpi=dpi, facecolor = '#FFFFFF')
self.ax = self.fig.add_subplot(111, sharex = sharex, sharey = sharey)
self.fig.subplots_adjust(left=0.15, bottom=0.15, right=0.9, top=0.9)
self.fig.add_axes(yscale='symlog')
self.xtitle=r"x-Axis"
self.ytitle=r"y-Axis"
self.PlotTitle = r"Title"
self.grid_status = True
self.xaxis_style = 'linear'
self.yaxis_style = 'linear'
#self.fig.yscale = 'log'
self.format_labels()
self.ax.hold(True)
FigureCanvas.__init__(self, self.fig)
#self.fc = FigureCanvas(self.fig)
#FigureCanvas.setSizePolicy(self,
# QSizePolicy.Expanding,
# QSizePolicy.Expanding)
FigureCanvas.updateGeometry(self)
def format_labels(self):
self.ax.set_title(self.PlotTitle)
self.ax.title.set_fontsize(5)
self.ax.set_xlabel(self.xtitle, fontsize = 4)
self.ax.set_ylabel(self.ytitle, fontsize = 4)
labels_x = self.ax.get_xticklabels()
labels_y = self.ax.get_yticklabels()
for xlabel in labels_x:
xlabel.set_fontsize(4)
for ylabel in labels_y:
ylabel.set_fontsize(4)
ylabel.set_color('b')
def sizeHint(self):
w, h = self.get_width_height()
return QSize(w, h)
def minimumSizeHint(self):
return QSize(10, 10)
def sizeHint(self):
w, h = self.get_width_height()
return QSize(w, h)
def minimumSizeHint(self):
return QSize(10, 10)
#mouseClick = pyqtProperty("QPoint",mouseClick,click)
class mplWidget(QWidget):
def __init__(self, parent = None):
QWidget.__init__(self, parent)
self.canvas = MyMplCanvas()
#self.toolbar = MyNavigationToolbar(self.canvas, self.canvas, direction = 'v')
self.hbox = QHBoxLayout()
#self.hbox.addWidget(self.toolbar)
self.hbox.addWidget(self.canvas)
self.setLayout(self.hbox)
def savePlot(self,filePath):
self.canvas.fig.savefig(filePath)
def setLegend(self,handle, label):
self.canvas.fig.legend(handle,label,'upper right')
def clearPlot(self):
self.canvas.fig.clear()
width = 10
height = 12
dpi = 125
sharex = None
sharey = None
self.canvas.fig = Figure(figsize = (width, height), dpi=dpi, facecolor = '#FFFFFF')
self.canvas.ax = self.canvas.fig.add_subplot(111, sharex = sharex, sharey = sharey)
self.canvas.fig.subplots_adjust(left=0.15, bottom=0.15, right=0.9, top=0.9)
self.canvas.fig.add_axes(yscale='symlog')
self.canvas.xtitle=r"x-Axis"
self.canvas.ytitle=r"y-Axis"
self.canvas.PlotTitle = r"Title"
self.canvas.grid_status = True
self.canvas.xaxis_style = 'linear'
self.canvas.yaxis_style = 'linear'
#self.fig.yscale = 'log'
self.canvas.format_labels()
self.canvas.ax.hold(True)
FigureCanvas.__init__(self.canvas, self.canvas.fig)
#self.fc = FigureCanvas(self.fig)
FigureCanvas.setSizePolicy(self,
QSizePolicy.Expanding,
QSizePolicy.Expanding)
FigureCanvas.updateGeometry(self)
Any Help would be greatly appreciated.
Answer: you can use aspect parameter of imshow() to adjust the ratio between the
height & weight:
from pylab import *
a = np.zeros((100,10)) # height=100, weight=10
subplot(211)
imshow(a) # ratio = 10
subplot(212)
imshow(a, aspect=0.1) # ratio = 1
show()
but it will stretch the image.
or you can use xlim(), ylim() the set the range of x-y axis.
imshow(a)
xlim(-50,50)
EDIT:
imshow() will set the aspect property of axe to "equal". you need reset it
before calling plot():
self.ui.mplWidget.canvas.ax.set_aspect("auto")
self.ui.mplWidget.canvas.ax.plot(self.xData,self.yData)
|
How can I use xml.sax module on an executable made with PyInstaller?
Question: I want to have my application read a document using xml.sax.parse. Things work
fine but when I move the executable to a Windows server 2008 machine things
break down. I get an SAXReaderNotAvailable exception with "No parsers found"
message.
The setup I'm using to build the executable is:
* 64 bit windows 7
* Python 2.7.2 32-bit
* PyInstaller 1.5.1
Answer: SAX readers seems to be dynamically imported, so the static analysis can't
detect them and they can't be embedded with application.
To correct this, you'll have to be explicit to force PyInstaller to import
those [hidden
modules](http://www.pyinstaller.org/export/latest/tags/1.5.1/doc/Manual.html?format=raw#listing-
hidden-imports).
Try to add this to you .spec (thanks Velociraptors) file :
hiddenimports = ['xml.sax.drivers', 'xml.sax.drivers2']
|
Download file from web in Python 3
Question: I am creating a program that will download a .jar (java) file from a web
server, by reading the URL that is specified in the .jad file of the same
game/application. I'm using Python 3.2.1
I've managed to extract the URL of the JAR file from the JAD file (every JAD
file contains the URL to the JAR file), but as you may imagine, the extracted
value is type() string.
Here's the relevant function:
def downloadFile(URL=None):
import httplib2
h = httplib2.Http(".cache")
resp, content = h.request(URL, "GET")
return content
downloadFile(URL_from_file)
However I always get an error saying that the type in the function above has
to be bytes, and not string. I've tried using the URL.encode('utf-8'), and
also bytes(URL,encoding='utf-8'), but I'd always get the same or similar
error.
So basically my question is how to download a file from a server when the URL
is stored in a string type?
Answer: If you want to obtain the contents of a web page into a variable, just `read`
the response of
[**`urllib.request.urlopen`**](http://docs.python.org/dev/library/urllib.request.html#urllib.request.urlopen):
import urllib.request
...
url = 'http://example.com/'
response = urllib.request.urlopen(url)
data = response.read() # a `bytes` object
text = data.decode('utf-8') # a `str`; this step can't be used if data is binary
* * *
The easiest way to download and save a file is to use the
[**`urllib.request.urlretrieve`**](http://docs.python.org/dev/library/urllib.request.html#urllib.request.urlretrieve)
function:
import urllib.request
...
# Download the file from `url` and save it locally under `file_name`:
urllib.request.urlretrieve(url, file_name)
import urllib.request
...
# Download the file from `url`, save it in a temporary directory and get the
# path to it (e.g. '/tmp/tmpb48zma.txt') in the `file_name` variable:
file_name, headers = urllib.request.urlretrieve(url)
But keep in mind that `urlretrieve` is considered
[legacy](http://docs.python.org/dev/library/urllib.request.html#legacy-
interface) and might become deprecated (not sure why, though).
So the most _correct_ way to do this would be to use the
[**`urllib.request.urlopen`**](http://docs.python.org/dev/library/urllib.request.html#urllib.request.urlopen)
function to return a file-like object that represents an HTTP response and
copy it to a real file using
[**`shutil.copyfileobj`**](http://docs.python.org/dev/library/shutil.html#shutil.copyfileobj).
import urllib.request
import shutil
...
# Download the file from `url` and save it locally under `file_name`:
with urllib.request.urlopen(url) as response, open(file_name, 'wb') as out_file:
shutil.copyfileobj(response, out_file)
If this seems too complicated, you may want to go simpler and store the whole
download in a `bytes` object and then write it to a file. But this works well
only for small files.
import urllib.request
...
# Download the file from `url` and save it locally under `file_name`:
with urllib.request.urlopen(url) as response, open(file_name, 'wb') as out_file:
data = response.read() # a `bytes` object
out_file.write(data)
* * *
It is possible to extract `.gz` (and maybe other formats) compressed data on
the fly, but such an operation probably requires the HTTP server to support
random access to the file.
import urllib.request
import gzip
...
# Read the first 64 bytes of the file inside the .gz archive located at `url`
url = 'http://example.com/something.gz'
with urllib.request.urlopen(url) as response:
with gzip.GzipFile(fileobj=response) as uncompressed:
file_header = uncompressed.read(64) # a `bytes` object
# Or do anything shown above using `uncompressed` instead of `response`.
|
regex result filter in python
Question: I am working on a program with regexes, I have to filter them but I can't find
out how. I want to match every red,xxxx or xxxx,red expression in my string
and put the colors xxxx into a group. Here is my code:
string = "blue,red red,yellow blue,yellow red,green purple red, ..."
regex = re.compile('(?:red,(?P<redfirst>\w+)|(?P<othercolorfirst>\w+),red)')
Then I write:
for match in regex.finditer(string):
if match.group('redfirst')!= "None":
print(match.group("redfirst"))
But I still obtain printing like:
None
yellow
green
None
I dont want the 'None' results to appear, I have to skip them in an smart way
if possible. Thanks for help!
**EDIT** None without quotes doesn't work either
Answer:
>>> import re
>>> regex = re.compile('(?:red,(?P<redfirst>\w+)|(?P<othercolorfirst>\w+),red)')
>>> string = "blue,red red,yellow blue,yellow red,green purple red, ..."
>>> for matches in regex.finditer(string):
... if matches.group('redfirst'):
... print matches.group('redfirst')
...
yellow
green
>>>
|
How to build debian package with CPack to execute setup.py?
Question: Until now, my project had only **.cpp** files that were compiled into
different binaries and I managed to configure **CPack** to build a proper
**debian package** without any problems.
Recently I wrote a couple of python applications and added them to the
project, as well as some custom modules that I would also like to incorporate
to the package.
After writing a `setup.py` script, I'm wondering how to add these files to the
**CPack** configuration in a way that `setup.py` get's executed automatically
when the user installs the package on the system with `dpkg -i package.deb`.
I'm struggling to find relevant information on how to configure CPack to
install custom python applications/modules. Has anyone tried this?
Answer: I figured out a way to do it but it's not very simple. I'll do my best to
explain the procedure so please be patient.
## The idea of this approach is to use _postinst_ and _prerm_ to install and
remove the python application from the system.
In the **CMakeLists.txt** that defines the project, you need to state that
**CPACK** is going to be used to generate a **.deb package**. There's some
variables that need to be filled with info related to the package itself, but
one named `CPACK_DEBIAN_PACKAGE_CONTROL_EXTRA` is very important because it's
used to specify the location of **postinst** and **prerm** , which are
standard scripts of the _debian packaging system_ that are automatically
executed by **dpkg** when the package is installed/removed.
At some point of your **main** `CMakeLists.txt` you should have something like
this:
add_subdirectory(name_of_python_app)
set(CPACK_COMPONENTS_ALL_IN_ONE_PACKAGE 1)
set(CPACK_PACKAGE_NAME "fake-package")
set(CPACK_PACKAGE_VENDOR "ACME")
set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "fake-package - brought to you by ACME")
set(CPACK_PACKAGE_VERSION "1.0.2")
set(CPACK_PACKAGE_VERSION_MAJOR "1")
set(CPACK_PACKAGE_VERSION_MINOR "0")
set(CPACK_PACKAGE_VERSION_PATCH "2")
SET(CPACK_SYSTEM_NAME "i386")
set(CPACK_GENERATOR "DEB")
set(CPACK_DEBIAN_PACKAGE_MAINTAINER "ACME Technology")
set(CPACK_DEBIAN_PACKAGE_DEPENDS "libc6 (>= 2.3.1-6), libgcc1 (>= 1:3.4.2-12), python2.6, libboost-program-options1.40.0 (>= 1.40.0)")
set(CPACK_DEBIAN_PACKAGE_CONTROL_EXTRA "${CMAKE_SOURCE_DIR}/name_of_python_app/postinst;${CMAKE_SOURCE_DIR}/name_of_python_app/prerm;")
set(CPACK_SET_DESTDIR "ON")
include(CPack)
Some of these variables are **optional** , but I'm filling them with info for
educational purposes.
Now, let's take a look at the scripts:
**postinst** :
#!/bin/sh
# postinst script for fake_python_app
set -e
cd /usr/share/pyshared/fake_package
sudo python setup.py install
**prerm** :
#!/bin/sh
# prerm script
#
# Removes all files installed by: ./setup.py install
sudo rm -rf /usr/share/pyshared/fake_package
sudo rm /usr/local/bin/fake_python_app
If you noticed, script **postinst** enters at
`/usr/share/pyshared/fake_package` and executes the **setup.py** that is
laying there to install the app on the system. Where does this file come from
and how it ends up there? This file is created by you and will be copied to
that location when your package is installed on the system. This action is
configured in `name_of_python_app/CMakeLists.txt`:
install(FILES setup.py
DESTINATION "/usr/share/pyshared/fake_package"
)
install(FILES __init__.py
DESTINATION "/usr/share/pyshared/fake_package/fake_package"
)
install(FILES fake_python_app
DESTINATION "/usr/share/pyshared/fake_package/fake_package"
)
install(FILES fake_module_1.py
DESTINATION "/usr/share/pyshared/fake_package/fake_package"
)
install(FILES fake_module_2.py
DESTINATION "/usr/share/pyshared/fake_package/fake_package"
)
As you can probably tell, besides the python application I want to install
there's also 2 custom python modules that I wrote that also need to be
installed. Below I describe the contents of the most important files:
**setup.py** :
#!/usr/bin/env python
from distutils.core import setup
setup(name='fake_package',
version='1.0.5',
description='Python modules used by fake-package',
py_modules=['fake_package.fake_module_1', 'fake_package.fake_module_2'],
scripts=['fake_package/fake_python_app']
)
**__init_ _.py**: is an empty file.
**fake_python_app** : your python application that will be installed in
/usr/local/bin
And that's pretty much it!
|
Problem with C library linked to Python interpreter, on Mac OS X
Question: I'm trying to use a C library that is supposed to be available from Python.
The library compiles fine on Mac OS X (10.6.0, i386) with GCC (version:
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5659).
When I try to import the python module from python, I get the error:
$ python
Enthought Python Distribution -- www.enthought.com
Version: 7.0-2 (64-bit)
Python 2.7.1 |EPD 7.0-2 (64-bit)| (r271:86832, Dec 3 2010, 15:56:20)
[GCC 4.0.1 (Apple Inc. build 5488)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>> import mymodule
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Library/Frameworks/EPD64.framework/Versions/7.0/lib/python2.7/site-packages/mymodule/__init__.py", line 2, in <module>
from mymodule import *
ImportError: dlopen(/Library/Frameworks/EPD64.framework/Versions/7.0/lib/python2.7/site-packages/mymodule/mymodule.so, 2): Symbol not found: _b_char
Referenced from: /Library/Frameworks/EPD64.framework/Versions/7.0/lib/python2.7/site-packages/mymodule/mymodule.so
Expected in: flat namespace
in /Library/Frameworks/EPD64.framework/Versions/7.0/lib/python2.7/site-packages/mymodule/mymodule.so
To respond to Ned's questions, this is the output I get:
$ file $(python -c 'import sys;print(sys.executable)')
/Library/Frameworks/EPD64.framework/Versions/Current/bin/python: Mach-O 64-bit executable x86_64
$ python -c 'import sys;print(sys.maxsize > 2**32)' ;
True
$ cd /Library/Frameworks/EPD64.framework/Versions/7.0/lib/python2.7/site-packages/mymodule
$ file mymodule.so
mymodule.so: Mach-O 64-bit bundle x86_64
$ otool -L mymodule.so
mymodule.so:
/usr/local/lib/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 125.2.1)
$ file /usr/lib/libSystem.B.dylib
/usr/lib/libSystem.B.dylib: Mach-O universal binary with 3 architectures
/usr/lib/libSystem.B.dylib (for architecture x86_64): Mach-O 64-bit dynamically linked shared library x86_64
/usr/lib/libSystem.B.dylib (for architecture i386): Mach-O dynamically linked shared library i386
/usr/lib/libSystem.B.dylib (for architecture ppc7400): Mach-O dynamically linked shared library ppc
$ file /usr/local/lib/libgcc_s.1.dylib
/usr/local/lib/libgcc_s.1.dylib: Mach-O universal binary with 4 architectures
/usr/local/lib/libgcc_s.1.dylib (for architecture i386): Mach-O dynamically linked shared library i386
/usr/local/lib/libgcc_s.1.dylib (for architecture x86_64): Mach-O 64-bit dynamically linked shared library x86_64
/usr/local/lib/libgcc_s.1.dylib (for architecture ppc): Mach-O dynamically linked shared library ppc
/usr/local/lib/libgcc_s.1.dylib (for architecture ppc64): Mach-O 64-bit dynamically linked shared library ppc64
It seems that there's a common architecture, but I'm unsure about whether
that's true for the libraries references by otool -L -- those seem to have
multiple versions.
Another thing I noticed is that when I make this package and compile it and
then make the Python module, the "build" directory of the module (i.e. the
directory at the same level as the setup.py file) has these Mac OS X _10.5_
files:
$ cd build/
$ ls
lib.macosx-10.5-x86_64-2.7 temp.macosx-10.5-x86_64-2.7
However, I am using Mac OS X 10.6. What controls which version is used to
compile a Python package using distutils? I'm afraid this might be causing the
problem.
Any idea what could be causing this? Thanks.
Answer: It is hard to know exactly what the problem is without more information but it
appears you are using a 64-bit version of Python (from EPD). Is the library
that you built also built as a 64-bit library? You should be able to tell by
doing something like this:
file $(python -c 'import sys;print(sys.executable)') # see archs that Python was built with
python -c 'import sys;print(sys.maxsize > 2**32)' ; # see if running as 64-bit (false if 32-bit)
cd /Library/Frameworks/EPD64.framework/Versions/7.0/lib/python2.7/site-packages/mymodule
file mymodule.so # see what architectures the C extension module is built with
otool -L mymodule.so # see what libraries are referenced by the C extension module
file /path/to/lib1 # see what archs the referenced lib module(s) are built with
There needs to be a common arch among all of them.
Update: Based on your additional information, the most suspicious looking item
is the library reference to `/usr/local/lib/libgcc_s.1.dylib`. That would seem
to indicate you have a local copy of `gcc` or other compiler installed in
`/usr/local`. Are you sure you aren't mixing compilers here? Try cleaning the
build directory and explicitly setting `export CC=/usr/bin/gcc-4.0` before
building your module. Or move that other compiler out of `/usr/local`. (The
10.5 thing should not be an issue. That just indicates that the EPD Python
distribution was built to run on 10.5 and later systems.)
|
Why aren't breakpoints working on the Swing Event Dispatch Thread in PyDev?
Question: I'm using Jython, Swing, and PyDev (Eclipse).
Breakpoints are not being hit on any code that runs on the EDT (aka AWT Event
Queue?).
This includes:
* Functions that are invoked from a Swing event (eg JButton click)
* Functions that, via a decorator, are run through `SwingUtilities.invokeLater()` (See the last example [here](http://wiki.python.org/jython/ADB%20SwingExamples#Decorator_to_add_a_function_to_SwingUtilities.invokeLater_donated_by_Alex_Gr.2BAPY-nholm).
* Functions that registered as hooks to a Java package (socket class), that I'm using.
**Swing event code to reproduce:**
from javax.swing import JFrame, JButton
def TestFunc(event):
#breakpoints in this function don't work
print "Hey"
if __name__ == '__main__':
mainWindow = JFrame('Test',
defaultCloseOperation = JFrame.EXIT_ON_CLOSE,
size = (1024, 600))
mainWindow.add(JButton("Hey", actionPerformed = TestFunc))
mainWindow.visible = True
**invokeLater() code to reproduce:**
from java.lang import Runnable
from javax.swing import SwingUtilities
import threading
class foo(Runnable):
def __init__(self, bar):
self.bar = bar
def run(self):
#breakpoints in this function don't work
print threading.currentThread()
print self.bar
if __name__ == '__main__':
myFoo = foo(5)
SwingUtilities.invokeLater(myFoo)
Answer: It's actually a Jython issue.
I.e.: in the code below, when TestFunc is called, the print from the
trace_dispatch should be called, but it's not.
So, the Jython tracing implementation is not calling the tracing function as
it should in that situation. You can 'help' the PyDev debugger by calling
`import pydevd;pydevd.settrace(suspend=False)` so that the debugger discovers
about that frame (i.e.: in the start of TestFunc add that line of code).
Note that if you don't pass the suspend=False, it'll act as a breakpoint in
the code and will stop the execution at that line.
import sys
import threading
def trace_dispatch(frame, event, arg):
print frame.f_code.co_filename, frame.f_code.co_name
sys.settrace(trace_dispatch)
threading.settrace(trace_dispatch)
from javax.swing import JFrame, JButton
def TestFunc(event):
print "Hey"
if __name__ == '__main__':
mainWindow = JFrame('Test',
defaultCloseOperation = JFrame.EXIT_ON_CLOSE,
size = (1024, 600))
mainWindow.add(JButton("Hey", actionPerformed = TestFunc))
mainWindow.visible = True
|
Instantiate all functions in Python
Question: Is there a way to do something like this:
util.py contains:
def add
def subtract
instantiate.py contains:
def instantiate
where instantiate does:
import util
def instantiate():
add = util.add
subtract = util.subtract
So I can skip typing `util` everytime I use a function and I can instantiate
them all using one function?
I tried but I get
NameError: global name 'util' is not defined
Answer: You can import specific functions from a module :
from util import add, substract
|
Regular expressions - C# behaves differently than Perl / Python
Question: Under Python:
ttsiod@elrond:~$ python
>>> import re
>>> a='This is a test'
>>> re.sub(r'(.*)', 'George', a)
'George'
Under Perl:
ttsiod@elrond:~$ perl
$a="This is a test";
$a=~s/(.*)/George/;
print $a;
(Ctrl-D)
George
Under C#:
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Text.RegularExpressions;
namespace IsThisACsharpBug
{
class Program
{
static void Main(string[] args)
{
var matchPattern = "(.*)";
var replacePattern = "George";
var newValue = Regex.Replace("This is nice", matchPattern, replacePattern);
Console.WriteLine(newValue);
}
}
}
Unfortunately, C# prints:
$ csc regexp.cs
Microsoft (R) Visual C# 2008 Compiler version 3.5.30729.5420
for Microsoft (R) .NET Framework version 3.5
Copyright (C) Microsoft Corporation. All rights reserved.
$ ./regexp.exe
GeorgeGeorge
Is this a bug in the regular expression library of C# ? Why does it print
"George" two times, when Perl and Python just print it once?
Answer: In your example the difference seems to be in the semantics of the 'replace'
function rather than in the regular expression processing itself.
.net is doing a "global" replace, i.e. it is replacing all matches rather than
just the first match.
**Global Replace in Perl**
(_notice the small 'g' at the end of the =~s line_)
$a="This is a test";
$a=~s/(.*)/George/g;
print $a;
which produces
GeorgeGeorge
**Single Replace in .NET**
var re = new Regex("(.*)");
var replacePattern = "George";
var newValue = re.Replace("This is nice", replacePattern, 1) ;
Console.WriteLine(newValue);
which produces
George
since it stops after the first replacement.
|
How do I get a reference for the current class object?
Question: In Python, how do I get a reference to the current class object within a class
statement? Example:
def setup_class_members(cls, prefix):
setattr(cls, prefix+"_var1", "hello")
setattr(cls, prefix+"_var2", "goodbye")
class myclass(object):
setup_class_members(cls, "coffee") # How to get "cls"?
def mytest(self):
print(self.coffee_var1)
print(self.coffee_var2)
x = myclass()
x.mytest()
>>> hello
>>> goodbye
Alternatives that I've written off are:
1. Use `locals()`: This gives a dict in a class statement that can be written to. This seems to work for classes, however the documentation tells you not to do this. (I might be tempted to go with this alternative if someone can assure me that this will continue to work for some time.)
2. Add members to the class object after the `class` statement: My actual application is to derive a PyQt4 `QWidget` class with dynamically created `pyqtProperty` class attributes. `QWidget` is unusual in that it has a custom metaclass. Very roughly, the metaclass compiles a list of `pyqtProperties` and stores it as additional member. For this reason, properties that are added to the class after creation have no effect. An example to clear this up:
from PyQt4 import QtCore, QtGui
# works
class MyWidget1(QtGui.QWidget):
myproperty = QtCore.pyqtProperty(int)
# doesn't work because QWidget's metaclass doesn't get to "compile" myproperty
class MyWidget2(QtGui.QWidget):
pass
MyWidget2.myproperty = QtCore.pyqtProperty(int)
Please note that the above will work for most programming cases; my case just
happens to be one of those unusual corner cases.
Answer: AFAIK there is two way to do what you want:
1. Using [metaclass](http://docs.python.org/reference/datamodel.html#customizing-class-creation), this will create your two variables in class creation time (which i think is what you want):
class Meta(type):
def __new__(mcs, name, bases, attr):
prefix = attr.get("prefix")
if prefix:
attr[prefix+"_var1"] = "hello"
attr[prefix+"_var2"] = "goodbye"
return type.__new__(mcs, name, bases, attr)
class myclass(object):
__metaclass__ = Meta
prefix = "coffee"
def mytest(self):
print(self.coffee_var1)
print(self.coffee_var2)
2. Create your two class variable in instantiation time:
class myclass(object): prefix = "coffee"
def __init__(self):
setattr(self.__class__, self.prefix+"_var1", "hello")
setattr(self.__class__, self.prefix+"_var2", "goodbye")
def mytest(self):
print(self.coffee_var1)
print(self.coffee_var2)
N.B: I'm not sure what you want to achieve because if you want to create
dynamic variables depending on the `prefix` variable why are you accessing
like you do in your `mytest` method ?! i hope it was just an example.
|
'No module named' error in Python while importing outside /home directory
Question: Probably this is a silly issue, but I haven't been able to figure it out.
I'm getting `ImportError: No module named etree.ElementTree` when I write:
#!/usr/bin/python3.2
import xml.etree.ElementTree as etree
tree = etree.parse('feed.xml')
root = tree.getroot()
If I run this same script in `/home/` or `/home/<user>/`, it works fine but
when my current working directory is
`/home/<user>/<some_directory>/<some_subdirectory>`, I get the above mentioned
error.
What is happening here?
Additional info: I'm running Ubuntu 11.04 and Python 3.2
Thanks in advance.
Answer: Try running Python in the place where it works and the place where it doesn't
work, and compare the values of `sys.path` when running Python in those two
locations.
My first guess would be that you have `$PYTHONSTARTUP` set to something that
depends on the working directory.
|
Convert sslsocket python code to ruby
Question: I have such code on python connect to some software by socket:
import socket, ssl
host = '127.0.0.1'
port = 8963
sert_key = '../keys/key.pem'
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, True)
sock.setsockopt(socket.SOL_TCP, socket.TCP_NODELAY, True)
sock.settimeout(30.5)
sock.connect((host, port))
sock = ssl.wrap_socket(sock, server_side=True, certfile=sert_key,
ssl_version=ssl.PROTOCOL_TLSv1)
cert = "hello"
cert = cert.encode('utf-8')
req = ('%08x'%len(cert))+cert
sock.sendall(req)
print sock.recv(4096)
Output: "OK", so its work.
I try to convert such code on ruby, but it doesn't work:
require 'socket'
require 'openssl'
host = '127.0.0.1'
port = 8963
sert_key = '../keys/key.pem'
socket = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
address = Socket.pack_sockaddr_in(port, host)
socket.setsockopt(Socket::SOL_SOCKET, Socket::SO_KEEPALIVE, true)
socket.setsockopt(Socket::SOL_TCP, Socket::TCP_NODELAY, true)
socket.connect(address)
#socket = TCPSocket.new(host, port) # not help also
ssl_context = OpenSSL::SSL::SSLContext.new(:TLSv1)
ssl_context.cert = OpenSSL::X509::Certificate.new(File.open(sert_key))
ssl_context.key = OpenSSL::PKey::RSA.new(File.open(sert_key))
ssl_context.verify_mode = OpenSSL::SSL::VERIFY_NONE
ssl_socket = OpenSSL::SSL::SSLSocket.new(socket, ssl_context)
ssl_socket.sync_close = true
ssl_socket.connect
sert = "hello"
sert = sert.force_encoding('UTF-8')
req = sprintf("%08x", sert.length) + sert
ssl_socket.write(req)
puts ssl_socket.read(4096)
But I have such error:
test1.rb:30:in `connect': SSL_connect returned=1 errno=0 state=SSLv3 read
server hello B: bad message type (OpenSSL::SSL::SSLError)
Help me please port this code on ruby. I don't understand what I miss (where
difference in codes).
P.S. Sorry, but software to which I want to connect not for sharing for now :(
Answer: Seems like you should use something like this:
require 'socket'
require 'openssl'
host = '127.0.0.1'
port = 8963
sert_key = '../keys/key.pem'
socket = TCPSocket.new(host, port) # not help also
ssl_context = OpenSSL::SSL::SSLContext.new(:TLSv1)
ssl_context.cert = OpenSSL::X509::Certificate.new(File.open(sert_key))
ssl_context.key = OpenSSL::PKey::RSA.new(File.open(sert_key))
ssl_context.verify_mode = OpenSSL::SSL::VERIFY_NONE
ssl_socket = OpenSSL::SSL::SSLSocket.new(socket, ssl_context)
ssl_socket.sync_close = true
ssl_socket.accept
sert = "hello"
sert = sert.force_encoding('UTF-8')
req = sprintf("%08x", sert.length) + sert
ssl_socket.write(req)
puts ssl_socket.sysread(4096)
**EDIT:** Updated code yet another time.
|
Set up Scrapy framework to run on Python 2.7
Question: Is it possible to select which version of Python is used by Scrapy? I am
running Scrapy on Ubuntu 10.04 which ships with Python 2.6. I have Python 2.7
installed on my machine and would like to take advantage of some of the
features of this later version but do not know how to set Scrapy to run on
2.7. When I type "python" into terminal, it runs Python 2.6 ("python2.7" loads
Python 2.7). Ideas?
Answer: The right way to do this is to organize things so that your special Python is
in its own subdirectory that has a bin and lib subdirectory. Then you put that
subdirectory in the `PATH` environment variable before the system binary
directories.
For instance, lets say you have a `/python directory` and you put the python
binary in `/python/bin/python`. Whether you do that by building python from
scratch, copying files, or linking to existing files, is not important. They
will all work. Note that it may not be enough to simply link to the existing
python2.7 binary since that will likely expect to find the Python libraries in
/python/lib if you run it this way.
Second step is to run `export PATH=/python/bin:$PATH`. You can type that at
the shell prompt to experiment, but longer term that should either go in a
`~/.profile` file, or in a special shell script used to run your application,
such as scrapy.
Note that a very popular way for Python developers to do this is to install
and setup virtualenv but if you aren't going to be changing environments every
day, that is probably overkill.
If you have this problem on a lot of machines then you might want to have a
custom build of Python that you can use everywhere such as [the portable
python built with this script](https://github.com/wavetossed/pybuild).
|
Django exception bugging me, don't know how to debug it
Question: I recently upgraded to python2.7 and django1.3 and since then
Unhandled exception in thread started by <bound method Command.inner_run of <django.core.management.commands.runserver.Command object at 0x109c57490>>
Traceback (most recent call last):
File "/Users/ApPeL/.virtualenvs/myhunt/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 88, in inner_run
self.validate(display_num_errors=True)
File "/Users/ApPeL/.virtualenvs/myhunt/lib/python2.7/site-packages/django/core/management/base.py", line 249, in validate
num_errors = get_validation_errors(s, app)
File "/Users/ApPeL/.virtualenvs/myhunt/lib/python2.7/site-packages/django/core/management/validation.py", line 36, in get_validation_errors
for (app_name, error) in get_app_errors().items():
File "/Users/ApPeL/.virtualenvs/myhunt/lib/python2.7/site-packages/django/db/models/loading.py", line 146, in get_app_errors
self._populate()
File "/Users/ApPeL/.virtualenvs/myhunt/lib/python2.7/site-packages/django/db/models/loading.py", line 67, in _populate
self.write_lock.release()
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 137, in release
raise RuntimeError("cannot release un-acquired lock")
RuntimeError: cannot release un-acquired lock
Your help would be greatly appreciated.
Answer: A usual first recommendation is to apply the latest updates to gevent or
greenlet or what you use related to threads. Implementation of
threading.Thread.start has been changed between Python 2.6 and 2.7. There are
many recipes how to start green... or green... with Django. Try to read any
recent for Python 2.7. and send a link which one makes the problem.
**Debugging:** Add following lines to your `manage.py` to enable logging of
thread start etc. to stderr:
import threading
setattr(threading, '__debug__', True)
Add the argument `verbose` to `django/db/loading.py` line 39 in order to see
also what threads acquire and release the lock.
- write_lock = threading.RLock(),
+ write_lock = threading.RLock(verbose=True),
Run development server. For only one thread without autoreload you should see
something like:
$ python manage.py runserver --noreload
Validating models...
MainThread: <_RLock owner='MainThread' count=1>.acquire(1): initial success
MainThread: <_RLock owner=None count=0>.release(): final release
Notes:
`count=1 acquire(1)` \-- the first acquire by a blocking lock
`owner=None count=0>.release()` \-- the the lock is currently being unlocked
$ python manage.py runserver
Validating models...
Dummy-1: <_RLock owner=-1222960272 count=1>.acquire(1): initial success
Dummy-1: <_RLock owner=None count=0>.release(): final release
This is the same with autoreload. Models are validated by the child process.
"Dummy-1" is a symbolic name of the thread. This can be repeated for more
threads, but no threads should/can acquire the lock until it is released by
the previous thread. We can continue according the results.
|
How to clear stdout in Python subprocess?
Question: this snippet will ping an ip address in windows and get output line each 2
seconds, however, I found there's a very slowly memory increasement of
ping.exe process after run it, if I deploy it to ping 1000 ip parallel, soon
it will cause server hang, I think it may because of stdout buffer, may I know
how to clear the stdout or limit its size? thanks!
...
proc = subprocess.Popen(['c:\windows\system32\ping.exe','127.0.0.1', '-l', '10000', '-t'],stdout=subprocess.PIPE, creationflags=subprocess.CREATE_NEW_PROCESS_GROUP)
while True:
time.sleep(2)
os.kill(proc.pid, signal.CTRL_BREAK_EVENT)
line = proc.stdout.readline()
Answer: ping is producing many more lines than you're reading due to the 2 second
timeout between reads. I'd move the os.kill call into another thread, and use
the main thread to read every line from `proc.stdout`:
import sys, os
import subprocess
import threading
import signal
import time
#Use ctrl-c and ctrl-break to terminate the script/ping
def sigbreak(signum, frame):
import sys
if proc.poll() is None:
print('Killing ping...')
proc.kill()
sys.exit(0)
signal.signal(signal.SIGBREAK, sigbreak)
signal.signal(signal.SIGINT, sigbreak)
#executes in a separate thread
def run(pid):
while True:
time.sleep(2)
try:
os.kill(pid, signal.CTRL_BREAK_EVENT)
except WindowsError:
#quit the thread if ping is dead
break
cmd = [r'c:\windows\system32\ping.exe', '127.0.0.1', '-l', '10000', '-t']
flags = subprocess.CREATE_NEW_PROCESS_GROUP
proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, creationflags=flags)
threading.Thread(target=run, args=(proc.pid,)).start()
while True:
line = proc.stdout.readline()
if b'statistics' in line:
#I don't know what you're doing with the ping stats.
#I'll just print them.
for n in range(4):
encoding = getattr(sys.stdout, 'encoding', 'ascii')
print(line.decode(encoding).rstrip())
line = proc.stdout.readline()
print()
|
mutagen: how to detect and embed album art in mp3, flac and mp4
Question: I'd like to be able to detect whether an audio file has embedded album art
and, if not, add album art to that file. I'm using mutagen
1) Detecting album art. Is there a simpler method than this pseudo code:
from mutagen import File
audio = File('music.ext')
test each of audio.pictures, audio['covr'] and audio['APIC:']
if doesn't raise an exception and isn't None, we found album art
2) I found this for embedding album art into an mp3 file: [How do you embed
album art into an MP3 using
Python?](http://stackoverflow.com/questions/409949/how-do-you-embed-album-art-
into-an-mp3-using-python)
How do I embed album art into other formats?
EDIT: embed mp4
audio = MP4(filename)
data = open(albumart, 'rb').read()
covr = []
if albumart.endswith('png'):
covr.append(MP4Cover(data, MP4Cover.FORMAT_PNG))
else:
covr.append(MP4Cover(data, MP4Cover.FORMAT_JPEG))
audio.tags['covr'] = covr
audio.save()
Answer: Embed flac:
from mutagen.flac import File, Picture, FLAC
def add_flac_cover(filename, albumart):
audio = File(filename)
image = Picture()
image.type = 3
if albumart.endswith('png'):
mime = 'image/png'
else:
mime = 'image/jpeg'
image.desc = 'front cover'
with open(albumart, 'rb') as f: # better than open(albumart, 'rb').read() ?
image.data = f.read()
audio.add_picture(image)
audio.save()
For completeness, detect picture
def pict_test(audio):
try:
x = audio.pictures
if x:
return True
except Exception:
pass
if 'covr' in audio or 'APIC:' in audio:
return True
return False
|
What does a . in an import statement in Python mean?
Question: I'm looking over the code for Python's `multiprocessing` module, and it
contains this line:
from ._multiprocessing import win32, Connection, PipeConnection
instead of
from _multiprocessing import win32, Connection, PipeConnection
the subtle difference being the period before `_multiprocessing`. What does
that mean? Why the period?
Answer: That's the new syntax for explicit [relative
imports](http://www.python.org/dev/peps/pep-0328/). It means import from the
current package.
|
Python dynamic class names
Question: > **Possible Duplicate:**
> [Dynamic loading of python
> modules](http://stackoverflow.com/questions/951124/dynamic-loading-of-
> python-modules)
> [python: How to add property to a class
> dynamically?](http://stackoverflow.com/questions/1325673/python-how-to-add-
> property-to-a-class-dynamically)
I have a dictionary with the filename and class names how can I import this
class names and how can I create this classes?
Example:
classNames = { 'MCTest':MCTestClass}
I want to import the MCTest and create the MCTestClass.
Answer: You have to use the `__import__` function:
[http://docs.python.org/library/functions.html#**import**](http://docs.python.org/library/functions.html#__import__)
Example from doc page:
>>> import sys
>>> name = 'foo.bar.baz'
>>> __import__(name)
<module 'foo' from ...>
>>> baz = sys.modules[name]
>>> baz
<module 'foo.bar.baz' from ...>
To instantiate a class from baz you should be able to do:
>>> SomeClass = getattr(baz, 'SomeClass')
>>> obj = SomeClass()
|
In Python, how do you find the index of the first value greater than a threshold in a sorted list?
Question: In Python, how do you find the index of the first value greater than a
threshold in a sorted list?
I can think of several ways of doing this (linear search, hand-written
dichotomy,..), but I'm looking for a clean an reasonably efficient way of
doing it. Since it's probably a pretty common problem, I'm sure experienced
SOers can help!
Thanks!
Answer: Have a look at [bisect](http://docs.python.org/library/bisect.html).
import bisect
l = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
bisect.bisect(l, 55) # returns 7
Compare it with linear search:
timeit bisect.bisect(l, 55)
# 375ns
timeit next((i for i,n in enumerate(l) if n > 55), len(l))
# 2.24us
timeit next((l.index(n) for n in l if n > 55), len(l))
# 1.93us
|
Control a specific pin on the Arduino Uno board using pyserial
Question: I have a python code that sends in a pattern, in which a light has to blink
in. (say eg. 101010. pattern may vary every time the code is run). when it is
executing this infinitely i want an interrupt( again sent by the python code
)to save the present conditions of the lights (say it is running 1 of the
sequence) and perform a specific task like turn off the lights for 10 seconds
and then resume the sequence. one way of doing this is by interrupting the
program by making the interrupt pin high. The question is can this making of
high/low controlled by the pyserial. So a simple pseudo code would be :
PYTHON part of the code:
Read the sequence:
Send the sequence to the arduino board using pyserial.
while(1)
{
Run a timer for 15 second.
When the timer overflows interrupt the arduino.
}
ARDUINO part of the code :
Read the sequence
while (1)
{
keep repeating the sequence on the LED.
}
// if interrupted on pin2 // assuming pin2 has the interrupt procedure
// Pyserial has to enable the interrupt WITHOUT using a switch for enabling the pin.
ISR
{
Save the present state of execution.
Turn off the LED.
}
# FOR A BETTER UNDERSTANDING :
I built up small codes to show the doubts i had :
CODE FOR THE ARDUINO IS :
int ledpin1 = 13;
int speedy;
int patterns;
void setup()
{
Serial.begin(9600);
Serial.print("Program Initiated: \n");
pinMode(ledpin1,OUTPUT);
//activate the blackout ISR when a interrupt is achieved at a certain pin. In this case pin2 of the arduino
attachInterrupt(0,blackout,CHANGE);
}
void loop()
{
if (Serial.available()>1)
{
Serial.print("starting loop \n");
patterns = Serial.read();
patterns = patterns-48;
speedy = Serial.read();
speedy = (speedy-48)*1000;
while(1)
{
patterns = !(patterns);
Serial.print(patterns);
digitalWrite(ledpin1,patterns);
delay(speedy);
}
}
}
/*
void blackout()
{
// ***Save the present state of the LED(on pin13)***
Serial.print ("The turning off LED's for performing the python code\n");
digitalWrite(ledpin,LOW);
//wait for the Python code to complete the task it wants to perform,
//so got to dealy the completion of the ISR
delay(2000);// delay the whole thing by 2 seconds
//***Continue with the while loop by setting the condition of the light to the saved condition.***
}
*/
==================================================================================
CODE FOR THE PYTHON FRONT IS :
import serial
import time
patterns=1
speedy=1
ser = serial.Serial()
ser.setPort("COM4")
ser.baudrate = 9600
ser.open()
def main():
if (ser.isOpen()):
#while(1):
ser.write(patterns)
ser.write(speedy)
blackoutfunc()
#ser.close()
def blackoutfunc():
while(1):
time.sleep(2)
print "Performing operations as required"
===============================================================================
Now the questions I had :
1) Is there a way to be able to activate the "blackout ISR" depending on the
conditions of a pin(in this case pin2 which is the INT0 pin) without using a
physical switch present on the pin. Hence the pin state has to be manipulated
by the software.
2) Is it possible to perform the operations as mentioned in the comments of
the blackout functions?
3) In the python code is it possible to just send in the data(i.e.
patterns,speedy) only once and make the arduino perform the pattern in a
infinite way without again sending the data by the `serial.write` command.
Hence avoiding the `while(1)` loop after the `ser.isOpen()`.
Answer: Have a look at this:
<https://github.com/ajfisher/arduino-command-server>
It's something I pulled together on the Arduino side to issue arbitrary
commands like switch a pin high / low and set PWM levels etc. It works over
both serial and network though it's a touch buggy on the network side at the
moment.
To use it, put the code on your arduino then you just write a python script
(or any other language that can use a serial connection) to connect over the
serial connection and then tell it what you want to do eg DIGW 1 HIGH etc
Also have a look at: <https://github.com/ajfisher/arduino-django-visualiser>
which is where I use a variation of this library to control some LEDs based on
some things going on in Django - it's more heavily python based.
|
Python regex: how to replace each instance of an occurrence with a different value?
Question: Suppose I have this string: `s = "blah blah blah"`
Using Python regex, how can I replace each instance of "blah" with a different
value (e.g. I have a list of values `v = ("1", "2", "3")`
Answer: You could use a [`re.sub`
callback](http://docs.python.org/library/re.html#re.sub):
import re
def callback(match):
return next(callback.v)
callback.v=iter(('1','2','3'))
s = "blah blah blah"
print(re.sub(r'blah',callback,s))
yields
1 2 3
|
Django South ignoring my custom rules
Question: I am using a custom Django model field to and widget to render a GoogleMap
widget in my admin, i also want to use South with my project to handle
database migrations. However after much effort i am unable to generate a
custom South rule that fits, this are my custom model and the last of the many
instrospection rules that i've tried.
class GoogleMapMarkerField(models.CharField):
__metaclass__ = models.SubfieldBase
description = _('Un marcador de Google Maps')
widget = GoogleMapMarkerWidget
def __init__(self, center, *args, **kwargs):
kwargs['max_length'] = 100
kwargs['help_text'] = _('Arrastre el cursor en el mapa para seleccionar el punto')
self.center = center
super(GoogleMapMarkerField, self).__init__(*args, **kwargs)
def formfield(self, **kwargs):
defaults = {
'center': self.center,
'form_class':GoogleMapMarkerFormField
}
defaults.update(kwargs)
return super(GoogleMapMarkerField, self).formfield(**defaults)
def to_python(self, value):
if isinstance(value, GoogleMapMarker):
return value
if isinstance(value, list):
return GoogleMapMarker(*map(float, value))
elif isinstance(value, basestring):
try:
return GoogleMapMarker(*map(float, value.split(',')))
except ValueError:
pass
def get_prep_value(self, value):
return '%f,%f' % (value.latitude, value.longitude)
add_introspection_rules([
(
(GoogleMapMarkerField, ),
[],
{
'center': ('center', {}),
}
)
], ["^website\.fields\.GoogleMapMarkerField"])
And this is the traceback that i'm getting
Traceback (most recent call last):
File "manage.py", line 14, in <module>
execute_manager(settings)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager
utility.execute()
File "/home/armonge/workspace/env/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv
self.execute(*args, **options.__dict__)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute
output = self.handle(*args, **options)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/management/commands/schemamigration.py", line 97, in handle
old_orm = last_migration.orm(),
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/utils.py", line 62, in method
value = function(self)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/migration/base.py", line 422, in orm
return FakeORM(self.migration_class(), self.app_label())
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/orm.py", line 46, in FakeORM
_orm_cache[args] = _FakeORM(*args)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/orm.py", line 125, in __init__
self.models[name] = self.make_model(app_label, model_name, data)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/orm.py", line 321, in make_model
field = self.eval_in_context(code, app, extra_imports)
File "/home/armonge/workspace/env/lib/python2.7/site-packages/south/orm.py", line 236, in eval_in_context
return eval(code, globals(), fake_locals)
File "<string>", line 1, in <module>
TypeError: __init__() takes at least 2 arguments (1 given)
Answer: `center` isn't a keyword argument, it's a positional argument. You shouldn't
use positional arguments with South, it doesn't understand them. (See [Custom
Fields: Keyword
Arguments](http://south.aeracode.org/docs/tutorial/part4.html#keyword-
arguments)). You could solve this by providing center with a default value(
`center=None` would be fine) and then following the example code at the link
for defining the keyword name as passed to `__init__`, the name as stored in
the database, and a dictionary of options (may be blank, but setting the
default value there too helps).
|
print redirected to file SOMETIMES results in incomplete printout in python
Question: I want to save list to a file so I cycle through it and write it to file.
Everything's fine. But SOMETIMES(!?!?) the list is not written entirely, it
stops rendering in the middle of the item. No error is raised, it silently
continues executing rest of the code. I've tried several ways to write it out,
several versions of python (2.4, 2.5, 2.7) and it's all the same. It sometimes
work, sometimes not. When it's printed out to the terminal window, not to the
file, it's working properly without glitches. Am I missing something?
this is it
...
from bpnn import *
...
# save input weights for later use:
writewtsi = open("c:/files/wtsi.txt", "w")
for i in range(net.ni):
print>>writewtsi, net.wi[i]
bpnn is neural network module from here: <http://python.ca/nas/python/bpnn.py>
Answer: Close the file when done with all the writes to ensure any write-caching is
flushed to the drive with:
writewtsi.close()
|
Python: How can I parse { apple: "1" , orange: "2" } into Dictionary?
Question: I have received an output , it likes this.
{
orange: '2',
apple: '1',
lemon: '3'
}
I know it is not a standard JSON format, but is it still possible to parse
into Python Dictionary type? Is it a must that **orange , apple , lemon** must
be quoted?
Thanks you
Answer: This is valid [YAML](http://en.wikipedia.org/wiki/YAML) (a superset of JSON).
Use [PyYAML](http://pyyaml.org/) to parse it:
>>> s = '''
... {
... orange: '2',
... apple: '1',
... lemon: '3'
... }'''
>>> import yaml
>>> yaml.load(s)
{'orange': '2', 'lemon': '3', 'apple': '1'}
More, since there is a tab space inside the string s, we better remove it
before parsing into yaml.
s=s.replace('\t','')
Otherwise, the above string cannot be parsed.
|
for loop ignores some elements of my list
Question: > **Possible Duplicate:**
> [Remove items from a list while iterating in
> Python](http://stackoverflow.com/questions/1207406/remove-items-from-a-list-
> while-iterating-in-python)
I want to remove all the dates in a list which are later than a given date. I
can't see why my method only removes some items of the list. Here's what I've
got:
import datetime
import numpy as np
import os
list_dates = [datetime.date(2012,1,3), datetime.date(2012,1,1), datetime.date(2012,1,5), datetime.date(2013,1,3), datetime.date(2013,1,1)]
for item in list_dates:
if item > datetime.date(2012,1,1):
list_dates.remove(item)
print list_dates
returns
[datetime.date(2012, 1, 1), datetime.date(2013, 1, 3)]
Answer: James and GWW are right, you cant modify the list while you are iterating
through the same. Instead copy the items which you want to keep to a new list.
list_dates = [datetime.date(2012,1,3), datetime.date(2012,1,1), datetime.date(2012,1,5), datetime.date(2013,1,3), datetime.date(2013,1,1)]
for item in list_dates:
if item < datetime.date(2012,1,1):
new_list_dates.add(item); // move this item (which you want to keep) to a new list.
print new_list_dates
|
python asynchronization
Question: Imagine a text file of 20 mb. I am reading char by char and extracting the
useful information. I have actually 2 main functions, one is reading the file
and the second is extracting the info. Something like this:
def reader(path):
f = open(path, 'r')
source = f.read()
f.close()
while True:
# here is where I read char by char and call the function extractor
def extractor(s):
# here I extract the useful information
Now, my goal is to continue to read while extractor is working. So basicaly,
my question is what is the appropriate way to accomplish my goal?
Answer: You can use producer/consumer threads. The threads can be synchronized using a
`Queue.Queue`.
**EDIT** : an example of a producer/consumer system:
from threading import Thread
from Queue import Queue
def produce(queue, n_items):
for d in range(n_items):
queue.put(d)
print "put {0} in queue".format(d)
def consume(queue, n_items):
d = 0
while d != n_items -1: # You need some sort of stop condition
d = queue.get()
print "got {0} from queue".format(d)
def start_producer_and_consumer(wait):
q = Queue()
consumer_thread = Thread(target = consume, args = (q, 10))
producer_thread = Thread(target = produce, args = (q, 10))
producer_thread.start()
consumer_thread.start()
if wait:
producer_thread.join()
consumer_thread.join()
if __name__ == '__main__':
start_producer_and_consumer(True)
As you will see if you execute this, everything will be consumed in the
correct order.
|
How should I handle working with celeryd_multi from code?
Question: So far, I've been working only with `python manage.py celeryd`, starting it
like this:
`python manage.py celeryd -l info --settings=settings`
The code from my view, does this:
BinaryExecTask.delay(request.POST["binary_path"])
And the code from my `settings.py`, is this:
import djcelery
djcelery.setup_loader()
BROKER_BACKEND = "djkombu.transport.DatabaseTransport"
#celery
BROKER_HOST = "localhost"
BROKER_PORT = 5672
BROKER_USER = "guest"
BROKER_PASSWORD = "guest"
BROKER_VHOST = "/"
and it will execute some binaries in the background. The thing is, some of the
binaries take pretty short time to run, while others may take up to half an
hour. Working with `celeryd`, all my tasks are blocked until the current one
finishes it's execution. I saw
[here](http://ask.github.com/celery/reference/celery.bin.celeryd_multi.html#examples)
some examples of starting celeryd_multi, but running:
`python manage.py celeryd_multi start 3 --settings=settings -l info`
gives this error:
celeryd-multi v2.3.1
> Starting nodes...
> celery1.x: Traceback (most recent call last):
File "manage.py", line 14, in <module>
execute_manager(settings)
File "c:\code\python27\lib\site-packages\django-1.3-py2.7.egg\django\core\management\_
line 438, in execute_manager
utility.execute()
File "c:\code\python27\lib\site-packages\django-1.3-py2.7.egg\django\core\management\_
line 379, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "c:\code\python27\lib\site-packages\django_celery-2.3.3-py2.7.egg\djcelery\manage
s\celeryd_multi.py", line 22, in run_from_argv
["%s %s" % (argv[0], argv[1])] + argv[2:])
File "c:\code\python27\lib\site-packages\celery-2.3.1-py2.7.egg\celery\bin\celeryd_mul
172, in execute_from_commandline
self.commands[argv[0]](argv[1:], cmd)
File "c:\code\python27\lib\site-packages\celery-2.3.1-py2.7.egg\celery\bin\celeryd_mul
205, in start
retcode = self.waitexec(argv)
File "c:\code\python27\lib\site-packages\celery-2.3.1-py2.7.egg\celery\bin\celeryd_mul
354, in waitexec
pipe = Popen(argstr, env=self.env)
File "c:\code\python27\lib\subprocess.py", line 672, in __init__
errread, errwrite)
File "c:\code\python27\lib\subprocess.py", line 882, in _execute_child
startupinfo)
WindowsError: [Error 2] The system cannot find the file specified
The `celeryd-multi start 3 -c 3` throws the same error. What should I do so
that I could succesfully start a celery instance that will allow me to run
more tasks in parallel? Also, would I need to do something different in my
view?
EDIT: some debugging led me here ( site-
packages\celery-2.3.1-py2.7.egg\celery\bin\celeryd_multi.py(354)waitexec )
351 def waitexec(self, argv, path=sys.executable):
352 args = " ".join([path] + list(argv))
353 -> argstr = shlex.split(args.encode("utf-8"))
354 pipe = Popen(argstr, env=self.env)
(Pdb) p argstr
['c:codepython27python.exe', 'manage.py', 'celeryd_detach', '-l', 'info', '--pidfile=celeryd@1.pid',
'-n', 'celery1.x', '--logfile=celeryd@1.log']
(Pdb) p Popen(argstr, env=self.env)
*** WindowsError: WindowsError(2, 'The system cannot find the file specified')
(Pdb)
So, as we can see, the path to Python gets destroyed :). What should I do
next?
EDIT2: I opened an issue [here](https://github.com/ask/celery/issues/472)
Answer: Looks like smth Windows-specific... Did you try to provide full path to python
executable in command line like
C:\code\python27\bin\python.exe manage.py celeryd_multi start 3 --settings=settings -l info
Also, use full paths for python file can be usefull
C:\code\python27\bin\python.exe C:\path\to\your\project\manage.py celeryd_multi start 3 --settings=settings -l info
|
Iterating a loop with a pause
Question: I am working to integrate with an API that has a limit on the number of
requests per second. Is there a way, when running a `for` loop in python to
delay each cycle? Conceptually, something like --
def function(request):
for x in [a,b,c,d,...]:
do something
wait y seconds
Thank you.
Answer:
import time
...
time.sleep(5)
This will sleep for 5 seconds. See
<http://docs.python.org/library/time.html#time.sleep>
|
Python pytz Converting a timestamp (string format) from one timezone to another
Question: I have a timestamp with timezone information in string format and I would like
to convert this to display the correct date/time using my local timezone. So
for eg... I have
timestamp1 = 2011-08-24 13:39:00 +0800
and I would like to convert this to say timezone offset +1000 to dsiplay
timestamp2 = 2011-08-24 15:39:00 +1000
I have tried using pytz but couldnt find many examples showing how to use the
offset information. One other link that I found on stackoverflow which depicts
this exact problem is [here](http://stackoverflow.com/questions/79797/how-do-
i-convert-local-time-to-utc-in-python). I was hoping there was some better way
I could handle this using pytz. Thanks for all suggestions in advance :).
**UPDATE**
Thanks Cixate. I just found the solution which is very similar to yours. Found
these links helpful - [LINK1](http://stackoverflow.com/questions/79797/how-do-
i-convert-local-time-to-utc-in-python) and
[LINK2](http://stackoverflow.com/questions/6729902/python-dateutil-parser-
fails)
Posting the solution for everyones benefit
from datetime import datetime
import sys, os
import pytz
from dateutil.parser import parse
datestr = "2011-09-09 13:20:00 +0800"
dt = parse(datestr)
print dt
localtime = dt.astimezone (pytz.timezone('Australia/Melbourne'))
print localtime.strftime ("%Y-%m-%d %H:%M:%S")
2011-09-09 15:20:00
Answer: [datetime.astimezone](http://docs.python.org/library/datetime.html#datetime.datetime.astimezone)
will do your basic conversion once you have a datetime object. If you're
trying to get a datetime object from a string, pip install [python-
dateutil](http://labix.org/python-dateutil) and it's as simple as:
>>> from dateutil.parser import parse
>>> from dateutil.tz import tzoffset
>>> dt = parse('2011-08-24 13:39:00 +0800')
datetime.datetime(2011, 8, 24, 13, 39, tzinfo=tzoffset(None, 28800))
>>> dt.astimezone(tzoffset(None, 3600))
datetime.datetime(2011, 8, 24, 6, 39, tzinfo=tzoffset(None, 3600))
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Python to parse non-standard XML file
Question: My input file is actually multiple XML files appending to one file. (It's from
[Google
Patents](http://commondatastorage.googleapis.com/patents/grantbib/2011/ipgb20110104_wk01.zip)).
It has below structure:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE us-patent-grant SYSTEM "us-patent-grant.dtd" [ ]>
<root_node>...</root_node>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE us-patent-grant SYSTEM "us-patent-grant.dtd" [ ]>
<root_node>...</root_node>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE us-patent-grant SYSTEM "us-patent-grant.dtd" [ ]>
<root_node>...</root_node>
Python xml.dom.minidom can't parse this non-standard file. What's a better way
to parse this file? I am not below code has good performance or not.
for line in infile:
if line == '<?xml version="1.0" encoding="UTF-8"?>':
xmldoc = minidom.parse(XMLstring)
else:
XMLstring += line
Answer: Here's my take on it, using a generator and `lxml.etree`. Extracted
information purely for example.
import urllib2, os, zipfile
from lxml import etree
def xmlSplitter(data,separator=lambda x: x.startswith('<?xml')):
buff = []
for line in data:
if separator(line):
if buff:
yield ''.join(buff)
buff[:] = []
buff.append(line)
yield ''.join(buff)
def first(seq,default=None):
"""Return the first item from sequence, seq or the default(None) value"""
for item in seq:
return item
return default
datasrc = "http://commondatastorage.googleapis.com/patents/grantbib/2011/ipgb20110104_wk01.zip"
filename = datasrc.split('/')[-1]
if not os.path.exists(filename):
with open(filename,'wb') as file_write:
r = urllib2.urlopen(datasrc)
file_write.write(r.read())
zf = zipfile.ZipFile(filename)
xml_file = first([ x for x in zf.namelist() if x.endswith('.xml')])
assert xml_file is not None
count = 0
for item in xmlSplitter(zf.open(xml_file)):
count += 1
if count > 10: break
doc = etree.XML(item)
docID = "-".join(doc.xpath('//publication-reference/document-id/*/text()'))
title = first(doc.xpath('//invention-title/text()'))
assignee = first(doc.xpath('//assignee/addressbook/orgname/text()'))
print "DocID: {0}\nTitle: {1}\nAssignee: {2}\n".format(docID,title,assignee)
Yields:
DocID: US-D0629996-S1-20110104
Title: Glove backhand
Assignee: Blackhawk Industries Product Group Unlimited LLC
DocID: US-D0629997-S1-20110104
Title: Belt sleeve
Assignee: None
DocID: US-D0629998-S1-20110104
Title: Underwear
Assignee: X-Technology Swiss GmbH
DocID: US-D0629999-S1-20110104
Title: Portion of compression shorts
Assignee: Nike, Inc.
DocID: US-D0630000-S1-20110104
Title: Apparel
Assignee: None
DocID: US-D0630001-S1-20110104
Title: Hooded shirt
Assignee: None
DocID: US-D0630002-S1-20110104
Title: Hooded shirt
Assignee: None
DocID: US-D0630003-S1-20110104
Title: Hooded shirt
Assignee: None
DocID: US-D0630004-S1-20110104
Title: Headwear cap
Assignee: None
DocID: US-D0630005-S1-20110104
Title: Footwear
Assignee: Vibram S.p.A.
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