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# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import copy
import logging
import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
from typing import List
from fairseq import utils
from fairseq.data import encoders
logger = logging.getLogger(__name__)
class BARTHubInterface(nn.Module):
"""A simple PyTorch Hub interface to BART.
Usage: https://github.com/pytorch/fairseq/tree/master/examples/bart
"""
def __init__(self, args, task, model):
super().__init__()
self.args = args
self.task = task
self.model = model
self.bpe = encoders.build_bpe(args)
self.max_positions = min(utils.resolve_max_positions(
self.task.max_positions(),
self.model.max_positions(),
))
# this is useful for determining the device
self.register_buffer('_float_tensor', torch.tensor([0], dtype=torch.float))
@property
def device(self):
return self._float_tensor.device
def encode(self, sentence: str, *addl_sentences, no_separator=True) -> torch.LongTensor:
"""
BPE-encode a sentence (or multiple sentences).
Every sequence begins with a beginning-of-sentence (`<s>`) symbol.
Every sentence ends with an end-of-sentence (`</s>`).
Example (single sentence): `<s> a b c </s>`
Example (sentence pair): `<s> d e f </s> 1 2 3 </s>`
The BPE encoding follows GPT-2. One subtle detail is that the GPT-2 BPE
requires leading spaces. For example::
>>> bart.encode('Hello world').tolist()
[0, 31414, 232, 2]
>>> bart.encode(' world').tolist()
[0, 232, 2]
>>> bart.encode('world').tolist()
[0, 8331, 2]
"""
tokens = self.bpe.encode(sentence)
if len(tokens.split(' ')) > self.max_positions - 2:
tokens = ' '.join(tokens.split(' ')[:self.max_positions - 2])
bpe_sentence = '<s> ' + tokens + ' </s>'
for s in addl_sentences:
bpe_sentence += (' </s>' if not no_separator else '')
bpe_sentence += ' ' + self.bpe.encode(s) + ' </s>'
tokens = self.task.source_dictionary.encode_line(bpe_sentence, append_eos=False)
return tokens.long()
def decode(self, tokens: torch.LongTensor):
assert tokens.dim() == 1
tokens = tokens.cpu().numpy()
if tokens[0] == self.task.source_dictionary.bos():
tokens = tokens[1:] # remove <s>
eos_mask = (tokens == self.task.source_dictionary.eos())
doc_mask = eos_mask[1:] & eos_mask[:-1]
sentences = np.split(tokens, doc_mask.nonzero()[0] + 1)
sentences = [self.bpe.decode(self.task.source_dictionary.string(s)) for s in sentences]
if len(sentences) == 1:
return sentences[0]
return sentences
def _build_sample(self, src_tokens: List[torch.LongTensor]):
# assert torch.is_tensor(src_tokens)
dataset = self.task.build_dataset_for_inference(
src_tokens,
[x.numel() for x in src_tokens],
)
sample = dataset.collater(dataset)
sample = utils.apply_to_sample(
lambda tensor: tensor.to(self.device),
sample
)
return sample
def sample(self, sentences: List[str], beam: int = 1, verbose: bool = False, **kwargs) -> str:
input = [self.encode(sentence) for sentence in sentences]
hypos = self.generate(input, beam, verbose, **kwargs)
return [self.decode(x['tokens']) for x in hypos]
def generate(self, tokens: List[torch.LongTensor], beam: int = 5, verbose: bool = False, **kwargs) -> torch.LongTensor:
sample = self._build_sample(tokens)
# build generator using current args as well as any kwargs
gen_args = copy.copy(self.args)
gen_args.beam = beam
for k, v in kwargs.items():
setattr(gen_args, k, v)
generator = self.task.build_generator([self.model], gen_args)
translations = self.task.inference_step(
generator,
[self.model],
sample,
prefix_tokens=sample['net_input']['src_tokens'].new_zeros((len(tokens), 1)).fill_(self.task.source_dictionary.bos()),
)
if verbose:
src_str_with_unk = self.string(tokens)
logger.info('S\t{}'.format(src_str_with_unk))
def getarg(name, default):
return getattr(gen_args, name, getattr(self.args, name, default))
# Process top predictions
hypos = [x[0] for x in translations]
hypos = [v for _, v in sorted(zip(sample['id'].tolist(), hypos))]
return hypos
def extract_features(self, tokens: torch.LongTensor, return_all_hiddens: bool = False) -> torch.Tensor:
if tokens.dim() == 1:
tokens = tokens.unsqueeze(0)
if tokens.size(-1) > min(self.model.max_positions()):
raise ValueError('tokens exceeds maximum length: {} > {}'.format(
tokens.size(-1), self.model.max_positions()
))
tokens.to(device=self.device),
prev_output_tokens = tokens.clone()
prev_output_tokens[:, 0] = tokens.gather(
1,
(tokens.ne(self.task.source_dictionary.pad()).sum(dim=1)- 1).unsqueeze(-1),
).squeeze()
prev_output_tokens[:, 1:] = tokens[:, :-1]
features, extra = self.model(
src_tokens=tokens,
src_lengths=None,
prev_output_tokens=prev_output_tokens,
features_only=True,
return_all_hiddens=return_all_hiddens,
)
if return_all_hiddens:
# convert from T x B x C -> B x T x C
inner_states = extra['inner_states']
return [inner_state.transpose(0, 1) for inner_state in inner_states]
else:
return features # just the last layer's features
def register_classification_head(
self, name: str, num_classes: int = None, embedding_size: int = None, **kwargs
):
self.model.register_classification_head(
name, num_classes=num_classes, embedding_size=embedding_size, **kwargs
)
def predict(self, head: str, tokens: torch.LongTensor, return_logits: bool = False):
if tokens.dim() == 1:
tokens = tokens.unsqueeze(0)
features = self.extract_features(tokens.to(device=self.device))
sentence_representation = features[
tokens.eq(self.task.source_dictionary.eos()), :
].view(features.size(0), -1, features.size(-1))[:, -1, :]
logits = self.model.classification_heads[head](sentence_representation)
if return_logits:
return logits
return F.log_softmax(logits, dim=-1)
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