Source code for

# Copyright 2019 The Texar Authors. All Rights Reserved.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
Pre-trained BERT tokenizer.

Code structure adapted from:

from typing import Any, Dict, List, Optional, Tuple

import os

from texar.torch.modules.pretrained.bert import PretrainedBERTMixin
from import TokenizerBase
from import \
    load_vocab, BasicTokenizer, WordpieceTokenizer
from texar.torch.hyperparams import HParams
from texar.torch.utils.utils import truncate_seq_pair

__all__ = [

[docs]class BERTTokenizer(PretrainedBERTMixin, TokenizerBase): r"""Pre-trained BERT Tokenizer. Args: pretrained_model_name (optional): a `str`, the name of pre-trained model (e.g., `bert-base-uncased`). Please refer to :class:`~texar.torch.modules.PretrainedBERTMixin` for all supported models. If None, the model name in :attr:`hparams` is used. cache_dir (optional): the path to a folder in which the pre-trained models will be cached. If `None` (default), a default directory (``texar_data`` folder under user's home directory) will be used. hparams (dict or HParams, optional): Hyperparameters. Missing hyperparameter will be set to default values. See :meth:`default_hparams` for the hyperparameter structure and default values. """ _IS_PRETRAINED = True _MAX_INPUT_SIZE = { # Standard BERT 'bert-base-uncased': 512, 'bert-large-uncased': 512, 'bert-base-cased': 512, 'bert-large-cased': 512, 'bert-base-multilingual-uncased': 512, 'bert-base-multilingual-cased': 512, 'bert-base-chinese': 512, # BioBERT 'biobert-v1.0-pmc': 512, 'biobert-v1.0-pubmed-pmc': 512, 'biobert-v1.0-pubmed': 512, 'biobert-v1.1-pubmed': 512, # SciBERT 'scibert-scivocab-uncased': 512, 'scibert-scivocab-cased': 512, 'scibert-basevocab-uncased': 512, 'scibert-basevocab-cased': 512, # SpanBERT 'spanbert-base-cased': 512, 'spanbert-large-cased': 512, } _VOCAB_FILE_NAMES = {'vocab_file': 'vocab.txt'} _VOCAB_FILE_MAP = { 'vocab_file': { # Standard BERT 'bert-base-uncased': 'vocab.txt', 'bert-large-uncased': 'vocab.txt', 'bert-base-cased': 'vocab.txt', 'bert-large-cased': 'vocab.txt', 'bert-base-multilingual-uncased': 'vocab.txt', 'bert-base-multilingual-cased': 'vocab.txt', 'bert-base-chinese': 'vocab.txt', # BioBERT 'biobert-v1.0-pmc': 'vocab.txt', 'biobert-v1.0-pubmed-pmc': 'vocab.txt', 'biobert-v1.0-pubmed': 'vocab.txt', 'biobert-v1.1-pubmed': 'vocab.txt', # SciBERT 'scibert-scivocab-uncased': 'vocab.txt', 'scibert-scivocab-cased': 'vocab.txt', 'scibert-basevocab-uncased': 'vocab.txt', 'scibert-basevocab-cased': 'vocab.txt', # SpanBERT 'spanbert-base-cased': 'vocab.txt', 'spanbert-large-cased': 'vocab.txt', } } def __init__(self, pretrained_model_name: Optional[str] = None, cache_dir: Optional[str] = None, hparams=None): # SpanBERT checkpoint files do not include vocabulary file, use # standard BERT directly when user use the pre-trained SpanBERT. if pretrained_model_name is not None: if pretrained_model_name.startswith('spanbert'): pretrained_model_name = pretrained_model_name.lstrip('span') elif hparams is not None: hparams = HParams(hparams, None) if hparams.pretrained_model_name is not None and \ hparams.pretrained_model_name.startswith('spanbert'): pretrained_model_name = \ hparams.pretrained_model_name.lstrip('span') self.load_pretrained_config(pretrained_model_name, cache_dir, hparams) super().__init__(hparams=None) self.config = { 'tokenize_chinese_chars': self.hparams['tokenize_chinese_chars'], 'do_lower_case': self.hparams['do_lower_case'], 'do_basic_tokenize': self.hparams['do_basic_tokenize'], 'non_split_tokens': self.hparams['non_split_tokens'], } if self.pretrained_model_dir is not None: assert self.pretrained_model_name is not None vocab_file = os.path.join(self.pretrained_model_dir, self._VOCAB_FILE_MAP['vocab_file'] [self.pretrained_model_name]) if self._MAX_INPUT_SIZE.get(self.pretrained_model_name): self.max_len = self._MAX_INPUT_SIZE[self.pretrained_model_name] else: vocab_file = self.hparams['vocab_file'] if self.hparams.get('max_len'): self.max_len = self.hparams['max_len'] if not os.path.isfile(vocab_file): raise ValueError("Can't find a vocabulary file at path " "'{}".format(vocab_file)) self.vocab = load_vocab(vocab_file) self.ids_to_tokens = dict((ids, tok) for tok, ids in self.vocab.items()) self.do_basic_tokenize = self.hparams['do_basic_tokenize'] if self.do_basic_tokenize: self.basic_tokenizer = BasicTokenizer( do_lower_case=self.hparams["do_lower_case"], never_split=self.hparams["non_split_tokens"], tokenize_chinese_chars=self.hparams["tokenize_chinese_chars"]) self.wordpiece_tokenizer = WordpieceTokenizer(vocab=self.vocab, unk_token=self.unk_token) def _map_text_to_token( # type: ignore self, text: str) -> List[str]: split_tokens: List[str] = [] if self.do_basic_tokenize: for token in self.basic_tokenizer.tokenize( text, never_split=self.all_special_tokens): assert token is not None for sub_token in self.wordpiece_tokenizer.tokenize(token): split_tokens.append(sub_token) else: split_tokens = self.wordpiece_tokenizer.tokenize(text) return split_tokens
[docs] def save_vocab(self, save_dir: str) -> Tuple[str]: r"""Save the tokenizer vocabulary to a directory or file.""" index = 0 if os.path.isdir(save_dir): save_dir = os.path.join(save_dir, self._VOCAB_FILE_NAMES['vocab_file']) with open(save_dir, "w", encoding="utf-8") as writer: for token, token_index in sorted(self.vocab.items(), key=lambda kv: kv[1]): if index != token_index: print("Saving vocabulary to {}: vocabulary indices are not " "consecutive. Please check that the vocabulary is " "not corrupted!".format(save_dir)) index = token_index writer.write(token + u'\n') index += 1 return (save_dir, )
@property def vocab_size(self) -> int: return len(self.vocab) def _map_token_to_id(self, token: str) -> int: r"""Maps a token to an id using the vocabulary.""" unk_id = self.vocab.get(self.unk_token) assert unk_id is not None return self.vocab.get(token, unk_id) def _map_id_to_token(self, index: int) -> str: r"""Maps an id to a token using the vocabulary. """ return self.ids_to_tokens.get(index, self.unk_token)
[docs] def map_token_to_text(self, tokens: List[str]) -> str: r"""Maps a sequence of tokens (string) to a single string.""" out_string = ' '.join(tokens).replace(' ##', '').strip() return out_string
[docs] def encode_text(self, text_a: str, text_b: Optional[str] = None, max_seq_length: Optional[int] = None) -> \ Tuple[List[int], List[int], List[int]]: r"""Adds special tokens to a sequence or sequence pair and computes the corresponding segment ids and input mask for BERT specific tasks. The sequence will be truncated if its length is larger than ``max_seq_length``. A BERT sequence has the following format: `[cls_token]` X `[sep_token]` A BERT sequence pair has the following format: `[cls_token]` A `[sep_token]` B `[sep_token]` Args: text_a: The first input text. text_b: The second input text. max_seq_length: Maximum sequence length. Returns: A tuple of `(input_ids, segment_ids, input_mask)`, where - ``input_ids``: A list of input token ids with added special token ids. - ``segment_ids``: A list of segment ids. - ``input_mask``: A list of mask ids. The mask has 1 for real tokens and 0 for padding tokens. Only real tokens are attended to. """ if max_seq_length is None: max_seq_length = self.max_len cls_token_id = self._map_token_to_id(self.cls_token) sep_token_id = self._map_token_to_id(self.sep_token) token_ids_a = self.map_text_to_id(text_a) assert isinstance(token_ids_a, list) token_ids_b = None if text_b: token_ids_b = self.map_text_to_id(text_b) if token_ids_b: assert isinstance(token_ids_b, list) # Modifies `token_ids_a` and `token_ids_b` in place so that the # total length is less than the specified length. # Account for [CLS], [SEP], [SEP] with "- 3" truncate_seq_pair(token_ids_a, token_ids_b, max_seq_length - 3) input_ids = ([cls_token_id] + token_ids_a + [sep_token_id] + token_ids_b + [sep_token_id]) segment_ids = [0] * (len(token_ids_a) + 2) + \ [1] * (len(token_ids_b) + 1) else: # Account for [CLS] and [SEP] with "- 2" token_ids_a = token_ids_a[:max_seq_length - 2] input_ids = [cls_token_id] + token_ids_a + [sep_token_id] segment_ids = [0] * len(input_ids) input_mask = [1] * len(input_ids) # Zero-pad up to the maximum sequence length. input_ids = input_ids + [0] * (max_seq_length - len(input_ids)) segment_ids = segment_ids + [0] * (max_seq_length - len(segment_ids)) input_mask = input_mask + [0] * (max_seq_length - len(input_mask)) assert len(input_ids) == max_seq_length assert len(segment_ids) == max_seq_length assert len(input_mask) == max_seq_length return input_ids, segment_ids, input_mask
[docs] @staticmethod def default_hparams() -> Dict[str, Any]: r"""Returns a dictionary of hyperparameters with default values. * The tokenizer is determined by the constructor argument :attr:`pretrained_model_name` if it's specified. In this case, `hparams` are ignored. * Otherwise, the tokenizer is determined by `hparams['pretrained_model_name']` if it's specified. All other configurations in `hparams` are ignored. * If the above two are `None`, the tokenizer is defined by the configurations in `hparams`. .. code-block:: python { "pretrained_model_name": "bert-base-uncased", "vocab_file": None, "max_len": 512, "unk_token": "[UNK]", "sep_token": "[SEP]", "pad_token": "[PAD]", "cls_token": "[CLS]", "mask_token": "[MASK]", "tokenize_chinese_chars": True, "do_lower_case": True, "do_basic_tokenize": True, "non_split_tokens": None, "name": "bert_tokenizer", } Here: `"pretrained_model_name"`: str or None The name of the pre-trained BERT model. `"vocab_file"`: str or None The path to a one-wordpiece-per-line vocabulary file. `"max_len"`: int The maximum sequence length that this model might ever be used with. `"unk_token"`: str Unknown token. `"sep_token"`: str Separation token. `"pad_token"`: str Padding token. `"cls_token"`: str Classification token. `"mask_token"`: str Masking token. `"tokenize_chinese_chars"`: bool Whether to tokenize Chinese characters. `"do_lower_case"`: bool Whether to lower case the input Only has an effect when `do_basic_tokenize=True` `"do_basic_tokenize"`: bool Whether to do basic tokenization before wordpiece. `"non_split_tokens"`: list List of tokens which will never be split during tokenization. Only has an effect when `do_basic_tokenize=True` `"name"`: str Name of the tokenizer. """ return { 'pretrained_model_name': 'bert-base-uncased', 'vocab_file': None, 'max_len': 512, 'unk_token': '[UNK]', 'sep_token': '[SEP]', 'pad_token': '[PAD]', 'cls_token': '[CLS]', 'mask_token': '[MASK]', 'tokenize_chinese_chars': True, 'do_lower_case': True, 'do_basic_tokenize': True, 'non_split_tokens': None, 'name': 'bert_tokenizer', '@no_typecheck': ['pretrained_model_name'], }
@classmethod def _transform_config(cls, pretrained_model_name: str, cache_dir: str): r"""Returns the configuration of the pre-trained BERT tokenizer.""" return { 'vocab_file': None, 'max_len': 512, 'unk_token': '[UNK]', 'sep_token': '[SEP]', 'pad_token': '[PAD]', 'cls_token': '[CLS]', 'mask_token': '[MASK]', 'tokenize_chinese_chars': True, 'do_lower_case': True, 'do_basic_tokenize': True, 'non_split_tokens': None, }