Source code for fairseq.tasks.language_modeling

# 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 logging
import os
from dataclasses import dataclass, field
from typing import Optional

import numpy as np
import torch
from fairseq import utils
from fairseq.data import (
    AppendTokenDataset,
    Dictionary,
    IdDataset,
    MonolingualDataset,
    NestedDictionaryDataset,
    NumelDataset,
    PadDataset,
    PrependTokenDataset,
    StripTokenDataset,
    TokenBlockDataset,
    TruncatedDictionary,
    data_utils,
)
from fairseq.data.indexed_dataset import get_available_dataset_impl
from fairseq.data.shorten_dataset import maybe_shorten_dataset
from fairseq.dataclass import ChoiceEnum, FairseqDataclass
from fairseq.tasks import LegacyFairseqTask, register_task
from omegaconf import II


SAMPLE_BREAK_MODE_CHOICES = ChoiceEnum(["none", "complete", "complete_doc", "eos"])
SHORTEN_METHOD_CHOICES = ChoiceEnum(["none", "truncate", "random_crop"])
logger = logging.getLogger(__name__)


@dataclass
class LanguageModelingConfig(FairseqDataclass):
    data: Optional[str] = field(
        default=None, metadata={"help": "path to data directory"}
    )
    sample_break_mode: SAMPLE_BREAK_MODE_CHOICES = field(
        default="none",
        metadata={
            "help": 'If omitted or "none", fills each sample with tokens-per-sample '
            'tokens. If set to "complete", splits samples only at the end '
            "of sentence, but may include multiple sentences per sample. "
            '"complete_doc" is similar but respects doc boundaries. '
            'If set to "eos", includes only one sentence per sample.'
        },
    )
    tokens_per_sample: int = field(
        default=1024,
        metadata={"help": "max number of tokens per sample for LM dataset"},
    )
    output_dictionary_size: int = field(
        default=-1, metadata={"help": "limit the size of output dictionary"}
    )
    self_target: bool = field(default=False, metadata={"help": "include self target"})
    future_target: bool = field(
        default=False, metadata={"help": "include future target"}
    )
    past_target: bool = field(default=False, metadata={"help": "include past target"})
    add_bos_token: bool = field(
        default=False, metadata={"help": "prepend beginning of sentence token (<s>)"}
    )
    max_target_positions: Optional[int] = field(
        default=None, metadata={"help": "max number of tokens in the target sequence"}
    )
    shorten_method: SHORTEN_METHOD_CHOICES = field(
        default="none",
        metadata={
            "help": "if not none, shorten sequences that exceed --tokens-per-sample"
        },
    )
    shorten_data_split_list: str = field(
        default="",
        metadata={
            "help": "comma-separated list of dataset splits to apply shortening to, "
            'e.g., "train,valid" (default: all dataset splits)'
        },
    )
    # TODO common vars below add to parent
    seed: int = II("common.seed")
    dataset_impl: Optional[ChoiceEnum(get_available_dataset_impl())] = II(
        "dataset.dataset_impl"
    )
    data_buffer_size: int = II("dataset.data_buffer_size")
    tpu: bool = II("common.tpu")


[docs]@register_task("language_modeling", dataclass=LanguageModelingConfig) class LanguageModelingTask(LegacyFairseqTask): """ Train a language model. Args: dictionary (~fairseq.data.Dictionary): the dictionary for the input of the language model output_dictionary (~fairseq.data.Dictionary): the dictionary for the output of the language model. In most cases it will be the same as *dictionary*, but could possibly be a more limited version of the dictionary (if ``--output-dictionary-size`` is used). targets (List[str]): list of the target types that the language model should predict. Can be one of "self", "future", and "past". Defaults to "future". .. note:: The language modeling task is compatible with :mod:`fairseq-train`, :mod:`fairseq-generate`, :mod:`fairseq-interactive` and :mod:`fairseq-eval-lm`. The language modeling task provides the following additional command-line arguments: .. argparse:: :ref: fairseq.tasks.language_modeling_parser :prog: """ def __init__(self, args, dictionary, output_dictionary=None, targets=None): super().__init__(args) self.dictionary = dictionary self.output_dictionary = output_dictionary or dictionary if targets is None: targets = ["future"] self.targets = targets @classmethod def setup_dictionary(cls, args, **kwargs): dictionary = None output_dictionary = None if args.data: paths = utils.split_paths(args.data) assert len(paths) > 0 dictionary = Dictionary.load(os.path.join(paths[0], "dict.txt")) logger.info("dictionary: {} types".format(len(dictionary))) output_dictionary = dictionary if args.output_dictionary_size >= 0: output_dictionary = TruncatedDictionary( dictionary, args.output_dictionary_size ) return (dictionary, output_dictionary) @classmethod def setup_task(cls, args, **kwargs): """Setup the task (e.g., load dictionaries). Args: args (argparse.Namespace): parsed command-line arguments """ dictionary, output_dictionary = cls.setup_dictionary(args, **kwargs) # upgrade old checkpoints if getattr(args, "exclude_self_target", False): args.self_target = False targets = [] if getattr(args, "self_target", False): targets.append("self") if getattr(args, "future_target", False): targets.append("future") if getattr(args, "past_target", False): targets.append("past") if len(targets) == 0: # standard language modeling targets = ["future"] return cls(args, dictionary, output_dictionary, targets=targets) def build_model(self, args): model = super().build_model(args) for target in self.targets: if target not in model.supported_targets: raise ValueError( "Unsupported language modeling target: {}".format(target) ) return model 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.args.data) assert len(paths) > 0 data_path = paths[(epoch - 1) % len(paths)] split_path = os.path.join(data_path, split) dataset = data_utils.load_indexed_dataset( split_path, self.dictionary, self.args.dataset_impl, combine=combine ) if dataset is None: raise FileNotFoundError( "Dataset not found: {} ({})".format(split, split_path) ) dataset = maybe_shorten_dataset( dataset, split, self.args.shorten_data_split_list, self.args.shorten_method, self.args.tokens_per_sample, self.args.seed, ) dataset = TokenBlockDataset( dataset, dataset.sizes, self.args.tokens_per_sample, pad=self.dictionary.pad(), eos=self.dictionary.eos(), break_mode=self.args.sample_break_mode, include_targets=True, ) add_eos_for_other_targets = ( self.args.sample_break_mode is not None and self.args.sample_break_mode != "none" ) self.datasets[split] = self._initialize_dataset( dataset=dataset, sizes=dataset.sizes, src_vocab=self.dictionary, tgt_vocab=self.output_dictionary, add_eos_for_other_targets=add_eos_for_other_targets, shuffle=True, targets=self.targets, add_bos_token=self.args.add_bos_token, ) def _initialize_dataset(self, **kwargs): return MonolingualDataset(**kwargs) def build_dataset_for_inference(self, src_tokens, src_lengths, **kwargs): """ Generate batches for inference. We prepend an eos token to src_tokens (or bos if `--add-bos-token` is set) and we append a <pad> to target. This is convenient both for generation with a prefix and LM scoring. """ dataset = StripTokenDataset( TokenBlockDataset( src_tokens, src_lengths, block_size=None, # ignored for "eos" break mode pad=self.source_dictionary.pad(), eos=self.source_dictionary.eos(), break_mode="eos", ), # remove eos from (end of) target sequence self.source_dictionary.eos(), ) src_dataset = PrependTokenDataset( dataset, token=( self.source_dictionary.bos() if getattr(self.args, "add_bos_token", False) else self.source_dictionary.eos() ), ) tgt_dataset = AppendTokenDataset(dataset, token=self.source_dictionary.pad()) return NestedDictionaryDataset( { "id": IdDataset(), "net_input": { "src_tokens": PadDataset( src_dataset, pad_idx=self.source_dictionary.pad(), left_pad=False, ), "src_lengths": NumelDataset(src_dataset, reduce=False), }, "target": PadDataset( tgt_dataset, pad_idx=self.source_dictionary.pad(), left_pad=False ), }, sizes=[np.array(src_lengths)], ) def inference_step( self, generator, models, sample, prefix_tokens=None, constraints=None ): with torch.no_grad(): # Generation will always be conditioned on bos_token if getattr(self.args, "add_bos_token", False): bos_token = self.source_dictionary.bos() else: bos_token = self.source_dictionary.eos() if constraints is not None: raise NotImplementedError( "Constrained decoding with the language_modeling task is not supported" ) # SequenceGenerator doesn't use src_tokens directly, we need to # pass the `prefix_tokens` argument instead if prefix_tokens is None and sample["net_input"]["src_tokens"].nelement(): prefix_tokens = sample["net_input"]["src_tokens"] if prefix_tokens[:, 0].eq(bos_token).all(): prefix_tokens = prefix_tokens[:, 1:] return generator.generate( models, sample, prefix_tokens=prefix_tokens, bos_token=bos_token ) @property def source_dictionary(self): """Return the :class:`~fairseq.data.Dictionary` for the language model.""" return self.dictionary @property def target_dictionary(self): """Return the :class:`~fairseq.data.Dictionary` for the language model.""" return self.output_dictionary