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"""Transformer language model.""" | |
from typing import Any | |
from typing import List | |
from typing import Tuple | |
import logging | |
import torch | |
import torch.nn as nn | |
import torch.nn.functional as F | |
from espnet.nets.lm_interface import LMInterface | |
from espnet.nets.pytorch_backend.transformer.embedding import PositionalEncoding | |
from espnet.nets.pytorch_backend.transformer.encoder import Encoder | |
from espnet.nets.pytorch_backend.transformer.mask import subsequent_mask | |
from espnet.nets.scorer_interface import BatchScorerInterface | |
from espnet.utils.cli_utils import strtobool | |
class TransformerLM(nn.Module, LMInterface, BatchScorerInterface): | |
"""Transformer language model.""" | |
def add_arguments(parser): | |
"""Add arguments to command line argument parser.""" | |
parser.add_argument( | |
"--layer", type=int, default=4, help="Number of hidden layers" | |
) | |
parser.add_argument( | |
"--unit", | |
type=int, | |
default=1024, | |
help="Number of hidden units in feedforward layer", | |
) | |
parser.add_argument( | |
"--att-unit", | |
type=int, | |
default=256, | |
help="Number of hidden units in attention layer", | |
) | |
parser.add_argument( | |
"--embed-unit", | |
type=int, | |
default=128, | |
help="Number of hidden units in embedding layer", | |
) | |
parser.add_argument( | |
"--head", type=int, default=2, help="Number of multi head attention" | |
) | |
parser.add_argument( | |
"--dropout-rate", type=float, default=0.5, help="dropout probability" | |
) | |
parser.add_argument( | |
"--att-dropout-rate", | |
type=float, | |
default=0.0, | |
help="att dropout probability", | |
) | |
parser.add_argument( | |
"--emb-dropout-rate", | |
type=float, | |
default=0.0, | |
help="emb dropout probability", | |
) | |
parser.add_argument( | |
"--tie-weights", | |
type=strtobool, | |
default=False, | |
help="Tie input and output embeddings", | |
) | |
parser.add_argument( | |
"--pos-enc", | |
default="sinusoidal", | |
choices=["sinusoidal", "none"], | |
help="positional encoding", | |
) | |
return parser | |
def __init__(self, n_vocab, args): | |
"""Initialize class. | |
Args: | |
n_vocab (int): The size of the vocabulary | |
args (argparse.Namespace): configurations. see py:method:`add_arguments` | |
""" | |
nn.Module.__init__(self) | |
# NOTE: for a compatibility with less than 0.9.7 version models | |
emb_dropout_rate = getattr(args, "emb_dropout_rate", 0.0) | |
# NOTE: for a compatibility with less than 0.9.7 version models | |
tie_weights = getattr(args, "tie_weights", False) | |
# NOTE: for a compatibility with less than 0.9.7 version models | |
att_dropout_rate = getattr(args, "att_dropout_rate", 0.0) | |
if args.pos_enc == "sinusoidal": | |
pos_enc_class = PositionalEncoding | |
elif args.pos_enc == "none": | |
def pos_enc_class(*args, **kwargs): | |
return nn.Sequential() # indentity | |
else: | |
raise ValueError(f"unknown pos-enc option: {args.pos_enc}") | |
self.embed = nn.Embedding(n_vocab, args.embed_unit) | |
if emb_dropout_rate == 0.0: | |
self.embed_drop = None | |
else: | |
self.embed_drop = nn.Dropout(emb_dropout_rate) | |
self.encoder = Encoder( | |
idim=args.embed_unit, | |
attention_dim=args.att_unit, | |
attention_heads=args.head, | |
linear_units=args.unit, | |
num_blocks=args.layer, | |
dropout_rate=args.dropout_rate, | |
attention_dropout_rate=att_dropout_rate, | |
input_layer="linear", | |
pos_enc_class=pos_enc_class, | |
) | |
self.decoder = nn.Linear(args.att_unit, n_vocab) | |
logging.info("Tie weights set to {}".format(tie_weights)) | |
logging.info("Dropout set to {}".format(args.dropout_rate)) | |
logging.info("Emb Dropout set to {}".format(emb_dropout_rate)) | |
logging.info("Att Dropout set to {}".format(att_dropout_rate)) | |
if tie_weights: | |
assert ( | |
args.att_unit == args.embed_unit | |
), "Tie Weights: True need embedding and final dimensions to match" | |
self.decoder.weight = self.embed.weight | |
def _target_mask(self, ys_in_pad): | |
ys_mask = ys_in_pad != 0 | |
m = subsequent_mask(ys_mask.size(-1), device=ys_mask.device).unsqueeze(0) | |
return ys_mask.unsqueeze(-2) & m | |
def forward( | |
self, x: torch.Tensor, t: torch.Tensor | |
) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]: | |
"""Compute LM loss value from buffer sequences. | |
Args: | |
x (torch.Tensor): Input ids. (batch, len) | |
t (torch.Tensor): Target ids. (batch, len) | |
Returns: | |
tuple[torch.Tensor, torch.Tensor, torch.Tensor]: Tuple of | |
loss to backward (scalar), | |
negative log-likelihood of t: -log p(t) (scalar) and | |
the number of elements in x (scalar) | |
Notes: | |
The last two return values are used | |
in perplexity: p(t)^{-n} = exp(-log p(t) / n) | |
""" | |
xm = x != 0 | |
if self.embed_drop is not None: | |
emb = self.embed_drop(self.embed(x)) | |
else: | |
emb = self.embed(x) | |
h, _ = self.encoder(emb, self._target_mask(x)) | |
y = self.decoder(h) | |
loss = F.cross_entropy(y.view(-1, y.shape[-1]), t.view(-1), reduction="none") | |
mask = xm.to(dtype=loss.dtype) | |
logp = loss * mask.view(-1) | |
logp = logp.sum() | |
count = mask.sum() | |
return logp / count, logp, count | |
def score( | |
self, y: torch.Tensor, state: Any, x: torch.Tensor | |
) -> Tuple[torch.Tensor, Any]: | |
"""Score new token. | |
Args: | |
y (torch.Tensor): 1D torch.int64 prefix tokens. | |
state: Scorer state for prefix tokens | |
x (torch.Tensor): encoder feature that generates ys. | |
Returns: | |
tuple[torch.Tensor, Any]: Tuple of | |
torch.float32 scores for next token (n_vocab) | |
and next state for ys | |
""" | |
y = y.unsqueeze(0) | |
if self.embed_drop is not None: | |
emb = self.embed_drop(self.embed(y)) | |
else: | |
emb = self.embed(y) | |
h, _, cache = self.encoder.forward_one_step( | |
emb, self._target_mask(y), cache=state | |
) | |
h = self.decoder(h[:, -1]) | |
logp = h.log_softmax(dim=-1).squeeze(0) | |
return logp, cache | |
# batch beam search API (see BatchScorerInterface) | |
def batch_score( | |
self, ys: torch.Tensor, states: List[Any], xs: torch.Tensor | |
) -> Tuple[torch.Tensor, List[Any]]: | |
"""Score new token batch (required). | |
Args: | |
ys (torch.Tensor): torch.int64 prefix tokens (n_batch, ylen). | |
states (List[Any]): Scorer states for prefix tokens. | |
xs (torch.Tensor): | |
The encoder feature that generates ys (n_batch, xlen, n_feat). | |
Returns: | |
tuple[torch.Tensor, List[Any]]: Tuple of | |
batchfied scores for next token with shape of `(n_batch, n_vocab)` | |
and next state list for ys. | |
""" | |
# merge states | |
n_batch = len(ys) | |
n_layers = len(self.encoder.encoders) | |
if states[0] is None: | |
batch_state = None | |
else: | |
# transpose state of [batch, layer] into [layer, batch] | |
batch_state = [ | |
torch.stack([states[b][i] for b in range(n_batch)]) | |
for i in range(n_layers) | |
] | |
if self.embed_drop is not None: | |
emb = self.embed_drop(self.embed(ys)) | |
else: | |
emb = self.embed(ys) | |
# batch decoding | |
h, _, states = self.encoder.forward_one_step( | |
emb, self._target_mask(ys), cache=batch_state | |
) | |
h = self.decoder(h[:, -1]) | |
logp = h.log_softmax(dim=-1) | |
# transpose state of [layer, batch] into [batch, layer] | |
state_list = [[states[i][b] for i in range(n_layers)] for b in range(n_batch)] | |
return logp, state_list | |