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| # SPDX-License-Identifier: MIT | |
| """ | |
| Commonly useful converters. | |
| """ | |
| import typing | |
| from ._compat import _AnnotationExtractor | |
| from ._make import NOTHING, Factory, pipe | |
| __all__ = [ | |
| "default_if_none", | |
| "optional", | |
| "pipe", | |
| "to_bool", | |
| ] | |
| def optional(converter): | |
| """ | |
| A converter that allows an attribute to be optional. An optional attribute | |
| is one which can be set to `None`. | |
| Type annotations will be inferred from the wrapped converter's, if it has | |
| any. | |
| Args: | |
| converter (typing.Callable): | |
| the converter that is used for non-`None` values. | |
| .. versionadded:: 17.1.0 | |
| """ | |
| def optional_converter(val): | |
| if val is None: | |
| return None | |
| return converter(val) | |
| xtr = _AnnotationExtractor(converter) | |
| t = xtr.get_first_param_type() | |
| if t: | |
| optional_converter.__annotations__["val"] = typing.Optional[t] | |
| rt = xtr.get_return_type() | |
| if rt: | |
| optional_converter.__annotations__["return"] = typing.Optional[rt] | |
| return optional_converter | |
| def default_if_none(default=NOTHING, factory=None): | |
| """ | |
| A converter that allows to replace `None` values by *default* or the result | |
| of *factory*. | |
| Args: | |
| default: | |
| Value to be used if `None` is passed. Passing an instance of | |
| `attrs.Factory` is supported, however the ``takes_self`` option is | |
| *not*. | |
| factory (typing.Callable): | |
| A callable that takes no parameters whose result is used if `None` | |
| is passed. | |
| Raises: | |
| TypeError: If **neither** *default* or *factory* is passed. | |
| TypeError: If **both** *default* and *factory* are passed. | |
| ValueError: | |
| If an instance of `attrs.Factory` is passed with | |
| ``takes_self=True``. | |
| .. versionadded:: 18.2.0 | |
| """ | |
| if default is NOTHING and factory is None: | |
| msg = "Must pass either `default` or `factory`." | |
| raise TypeError(msg) | |
| if default is not NOTHING and factory is not None: | |
| msg = "Must pass either `default` or `factory` but not both." | |
| raise TypeError(msg) | |
| if factory is not None: | |
| default = Factory(factory) | |
| if isinstance(default, Factory): | |
| if default.takes_self: | |
| msg = "`takes_self` is not supported by default_if_none." | |
| raise ValueError(msg) | |
| def default_if_none_converter(val): | |
| if val is not None: | |
| return val | |
| return default.factory() | |
| else: | |
| def default_if_none_converter(val): | |
| if val is not None: | |
| return val | |
| return default | |
| return default_if_none_converter | |
| def to_bool(val): | |
| """ | |
| Convert "boolean" strings (for example, from environment variables) to real | |
| booleans. | |
| Values mapping to `True`: | |
| - ``True`` | |
| - ``"true"`` / ``"t"`` | |
| - ``"yes"`` / ``"y"`` | |
| - ``"on"`` | |
| - ``"1"`` | |
| - ``1`` | |
| Values mapping to `False`: | |
| - ``False`` | |
| - ``"false"`` / ``"f"`` | |
| - ``"no"`` / ``"n"`` | |
| - ``"off"`` | |
| - ``"0"`` | |
| - ``0`` | |
| Raises: | |
| ValueError: For any other value. | |
| .. versionadded:: 21.3.0 | |
| """ | |
| if isinstance(val, str): | |
| val = val.lower() | |
| if val in (True, "true", "t", "yes", "y", "on", "1", 1): | |
| return True | |
| if val in (False, "false", "f", "no", "n", "off", "0", 0): | |
| return False | |
| msg = f"Cannot convert value to bool: {val!r}" | |
| raise ValueError(msg) | |