tokenizer.py

# coding=utf-8
# Copyright (c) 2019, NVIDIA CORPORATION.  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
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Megatron tokenizer."""

from abc import ABC
from abc import abstractmethod

from megatron.arguments import get_args
from .bert_tokenization import FullTokenizer as FullBertTokenizer


def build_tokenizer():
    """Initialize tokenizer."""

    # Retrieve args.
    args = get_args()

    if args.rank == 0:
        print('building {} tokenizer ...'.format(args.tokenizer_type),
              flush=True)

    # Select and instantiate the tokenizer.
    if args.tokenizer_type == 'BertWordPieceLowerCase':
        tokenizer = _BertWordPieceTokenizer(vocab_file=args.vocab_file,
                                                    lower_case=True)
    else:
        raise NotImplementedError('{} tokenizer is not '
                                  'implemented.'.format(args.tokenizer_type))

    # Add vocab size.
    args.padded_vocab_size = _vocab_size_with_padding(tokenizer.vocab_size)

    return tokenizer


def _vocab_size_with_padding(orig_vocab_size):
    """Pad vocab size so it is divisible by model parallel size and
    still having GPU friendly size."""

    args = get_args()
    after = orig_vocab_size
    multiple = args.make_vocab_size_divisible_by * \
               args.model_parallel_size
    while (after % multiple) != 0:
        after += 1
    if args.rank == 0:
        print(' > padded vocab (size: {}) with {} dummy tokens '
              '(new size: {})'.format(
                  orig_vocab_size, after - orig_vocab_size, after), flush=True)
    return after


class AbstractTokenizer(ABC):
    """Abstract class for tokenizer."""

    def __init__(self, name):
        self.name = name
        super().__init__()

    @property
    @abstractmethod
    def vocab_size(self):
        pass

    @abstractmethod
    def tokenize(self, text):
        pass

    @property
    def cls(self):
        raise NotImplementedError('CLS is not provided for {} '
                                  'tokenizer'.format(self.name))

    @property
    def sep(self):
        raise NotImplementedError('SEP is not provided for {} '
                                  'tokenizer'.format(self.name))

    @property
    def pad(self):
        raise NotImplementedError('PAD is not provided for {} '
                                  'tokenizer'.format(self.name))

    @property
    def eod(self):
        raise NotImplementedError('EOD is not provided for {} '
                                  'tokenizer'.format(self.name))



class _BertWordPieceTokenizer(AbstractTokenizer):
    """Original BERT wordpiece tokenizer."""

    def __init__(self, vocab_file, lower_case=True):
        if lower_case:
            name = 'BERT Lower Case'
        else:
            name = 'BERT Upper Case'
        super().__init__(name)
        self.tokenizer = FullBertTokenizer(vocab_file, do_lower_case=lower_case)
        self.cls_id = self.tokenizer.vocab['[CLS]']
        self.sep_id = self.tokenizer.vocab['[SEP]']
        self.pad_id = self.tokenizer.vocab['[PAD]']

    @property
    def vocab_size(self):
        return self.tokenizer.vocab_size()

    def tokenize(self, text):
        text_tokens = self.tokenizer.tokenize(text)
        return self.tokenizer.convert_tokens_to_ids(text_tokens)

    @property
    def cls(self):
        return self.cls_id

    @property
    def sep(self):
        return self.sep_id

    @property
    def pad(self):
        return self.pad_id