BERT.py

from torch import nn
from transformers import BertModel, BertTokenizer
import json
from typing import List
import os
import numpy as np
import logging

class BERT(nn.Module):
    """BERT model to generate token embeddings.

    Each token is mapped to an output vector from BERT.
    """
    def __init__(self, model_name_or_path: str, max_seq_length: int = 128, do_lower_case: bool = True):
        super(BERT, self).__init__()
        self.config_keys = ['max_seq_length', 'do_lower_case']
        self.do_lower_case = do_lower_case

        if max_seq_length > 510:
            logging.warning("BERT only allows a max_seq_length of 510 (512 with special tokens). Value will be set to 510")
            max_seq_length = 510
        self.max_seq_length = max_seq_length

        self.bert = BertModel.from_pretrained(model_name_or_path)
        self.tokenizer = BertTokenizer.from_pretrained(model_name_or_path, do_lower_case=do_lower_case)
        self.cls_token_id = self.tokenizer.convert_tokens_to_ids([self.tokenizer.cls_token])[0]
        self.sep_token_id = self.tokenizer.convert_tokens_to_ids([self.tokenizer.sep_token])[0]

    def forward(self, features):
        """Returns token_embeddings, cls_token"""
        output_tokens = self.bert(input_ids=features['input_ids'], token_type_ids=features['token_type_ids'], attention_mask=features['input_mask'])[0]
        cls_tokens = output_tokens[:, 0, :]  # CLS token is first token
        features.update({'token_embeddings': output_tokens, 'cls_token_embeddings': cls_tokens, 'input_mask': features['input_mask']})
        return features

    def get_word_embedding_dimension(self) -> int:
        return self.bert.config.hidden_size

    def tokenize(self, text: str) -> List[int]:
        """
        Tokenizes a text and maps tokens to token-ids
        """
        return self.tokenizer.convert_tokens_to_ids(self.tokenizer.tokenize(text))

    def get_sentence_features(self, tokens: List[int], pad_seq_length: int):
        """
        Convert tokenized sentence in its embedding ids, segment ids and mask

        :param tokens:
            a tokenized sentence
        :param pad_seq_length:
            the maximal length of the sequence. Cannot be greater than self.sentence_transformer_config.max_seq_length
        :return: embedding ids, segment ids and mask for the sentence
        """
        pad_seq_length = min(pad_seq_length, self.max_seq_length)

        tokens = tokens[:pad_seq_length]
        input_ids = [self.cls_token_id] + tokens + [self.sep_token_id]
        sentence_length = len(input_ids)

        pad_seq_length += 2  ##Add Space for CLS + SEP token

        token_type_ids = [0] * len(input_ids)
        input_mask = [1] * len(input_ids)

        # Zero-pad up to the sequence length. BERT: Pad to the right
        padding = [0] * (pad_seq_length - len(input_ids))
        input_ids += padding
        token_type_ids += padding
        input_mask += padding

        assert len(input_ids) == pad_seq_length
        assert len(input_mask) == pad_seq_length
        assert len(token_type_ids) == pad_seq_length

        return {'input_ids': np.asarray(input_ids, dtype=np.int64), 'token_type_ids': np.asarray(token_type_ids, dtype=np.int64), 'input_mask': np.asarray(input_mask, dtype=np.int64), 'sentence_lengths': np.asarray(sentence_length, dtype=np.int64)}

    def get_config_dict(self):
        return {key: self.__dict__[key] for key in self.config_keys}

    def save(self, output_path: str):
        self.bert.save_pretrained(output_path)
        self.tokenizer.save_pretrained(output_path)

        with open(os.path.join(output_path, 'sentence_bert_config.json'), 'w') as fOut:
            json.dump(self.get_config_dict(), fOut, indent=2)

    @staticmethod
    def load(input_path: str):
        with open(os.path.join(input_path, 'sentence_bert_config.json')) as fIn:
            config = json.load(fIn)
        return BERT(model_name_or_path=input_path, **config)