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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.
from dataclasses import dataclass, field
import torch
from fairseq import utils
from fairseq.data import LanguagePairDataset
from fairseq.dataclass import ChoiceEnum
from fairseq.tasks import register_task
from fairseq.tasks.translation import (
TranslationConfig,
TranslationTask,
load_langpair_dataset,
)
from fairseq.utils import new_arange
NOISE_CHOICES = ChoiceEnum(["random_delete", "random_mask", "no_noise", "full_mask"])
@dataclass
class TranslationLevenshteinConfig(TranslationConfig):
noise: NOISE_CHOICES = field(
default="random_delete",
metadata={"help": "type of noise"},
)
@register_task("translation_lev", dataclass=TranslationLevenshteinConfig)
class TranslationLevenshteinTask(TranslationTask):
"""
Translation (Sequence Generation) task for Levenshtein Transformer
See `"Levenshtein Transformer" <https://arxiv.org/abs/1905.11006>`_.
"""
cfg: TranslationLevenshteinConfig
def load_dataset(self, split, epoch=1, combine=False, **kwargs):
"""Load a given dataset split.
Args:
split (str): name of the split (e.g., train, valid, test)
"""
paths = utils.split_paths(self.cfg.data)
assert len(paths) > 0
data_path = paths[(epoch - 1) % len(paths)]
# infer langcode
src, tgt = self.cfg.source_lang, self.cfg.target_lang
self.datasets[split] = load_langpair_dataset(
data_path,
split,
src,
self.src_dict,
tgt,
self.tgt_dict,
combine=combine,
dataset_impl=self.cfg.dataset_impl,
upsample_primary=self.cfg.upsample_primary,
left_pad_source=self.cfg.left_pad_source,
left_pad_target=self.cfg.left_pad_target,
max_source_positions=self.cfg.max_source_positions,
max_target_positions=self.cfg.max_target_positions,
prepend_bos=True,
)
def inject_noise(self, target_tokens):
def _random_delete(target_tokens):
pad = self.tgt_dict.pad()
bos = self.tgt_dict.bos()
eos = self.tgt_dict.eos()
max_len = target_tokens.size(1)
target_mask = target_tokens.eq(pad)
target_score = target_tokens.clone().float().uniform_()
target_score.masked_fill_(
target_tokens.eq(bos) | target_tokens.eq(eos), 0.0
)
target_score.masked_fill_(target_mask, 1)
target_score, target_rank = target_score.sort(1)
target_length = target_mask.size(1) - target_mask.float().sum(
1, keepdim=True
)
# do not delete <bos> and <eos> (we assign 0 score for them)
target_cutoff = (
2
+ (
(target_length - 2)
* target_score.new_zeros(target_score.size(0), 1).uniform_()
).long()
)
target_cutoff = target_score.sort(1)[1] >= target_cutoff
prev_target_tokens = (
target_tokens.gather(1, target_rank)
.masked_fill_(target_cutoff, pad)
.gather(1, target_rank.masked_fill_(target_cutoff, max_len).sort(1)[1])
)
prev_target_tokens = prev_target_tokens[
:, : prev_target_tokens.ne(pad).sum(1).max()
]
return prev_target_tokens
def _random_mask(target_tokens):
pad = self.tgt_dict.pad()
bos = self.tgt_dict.bos()
eos = self.tgt_dict.eos()
unk = self.tgt_dict.unk()
target_masks = (
target_tokens.ne(pad) & target_tokens.ne(bos) & target_tokens.ne(eos)
)
target_score = target_tokens.clone().float().uniform_()
target_score.masked_fill_(~target_masks, 2.0)
target_length = target_masks.sum(1).float()
target_length = target_length * target_length.clone().uniform_()
target_length = target_length + 1 # make sure to mask at least one token.
_, target_rank = target_score.sort(1)
target_cutoff = new_arange(target_rank) < target_length[:, None].long()
prev_target_tokens = target_tokens.masked_fill(
target_cutoff.scatter(1, target_rank, target_cutoff), unk
)
return prev_target_tokens
def _full_mask(target_tokens):
pad = self.tgt_dict.pad()
bos = self.tgt_dict.bos()
eos = self.tgt_dict.eos()
unk = self.tgt_dict.unk()
target_mask = (
target_tokens.eq(bos) | target_tokens.eq(eos) | target_tokens.eq(pad)
)
return target_tokens.masked_fill(~target_mask, unk)
if self.cfg.noise == "random_delete":
return _random_delete(target_tokens)
elif self.cfg.noise == "random_mask":
return _random_mask(target_tokens)
elif self.cfg.noise == "full_mask":
return _full_mask(target_tokens)
elif self.cfg.noise == "no_noise":
return target_tokens
else:
raise NotImplementedError
def build_generator(self, models, args, **unused):
# add models input to match the API for SequenceGenerator
from fairseq.iterative_refinement_generator import IterativeRefinementGenerator
return IterativeRefinementGenerator(
self.target_dictionary,
eos_penalty=getattr(args, "iter_decode_eos_penalty", 0.0),
max_iter=getattr(args, "iter_decode_max_iter", 10),
beam_size=getattr(args, "iter_decode_with_beam", 1),
reranking=getattr(args, "iter_decode_with_external_reranker", False),
decoding_format=getattr(args, "decoding_format", None),
adaptive=not getattr(args, "iter_decode_force_max_iter", False),
retain_history=getattr(args, "retain_iter_history", False),
)
def build_dataset_for_inference(self, src_tokens, src_lengths, constraints=None):
if constraints is not None:
# Though see Susanto et al. (ACL 2020): https://www.aclweb.org/anthology/2020.acl-main.325/
raise NotImplementedError(
"Constrained decoding with the translation_lev task is not supported"
)
return LanguagePairDataset(
src_tokens, src_lengths, self.source_dictionary, append_bos=True
)
def train_step(
self, sample, model, criterion, optimizer, update_num, ignore_grad=False
):
model.train()
sample["prev_target"] = self.inject_noise(sample["target"])
loss, sample_size, logging_output = criterion(model, sample)
if ignore_grad:
loss *= 0
optimizer.backward(loss)
return loss, sample_size, logging_output
def valid_step(self, sample, model, criterion):
model.eval()
with torch.no_grad():
sample["prev_target"] = self.inject_noise(sample["target"])
loss, sample_size, logging_output = criterion(model, sample)
return loss, sample_size, logging_output
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