sentence_transformers/models/Transformer.py

from torch import nn
from transformers import AutoModel, AutoTokenizer, AutoConfig, T5Config, MT5Config
import json
from typing import List, Dict, Optional, Union, Tuple
import os


class Transformer(nn.Module):
    """Huggingface AutoModel to generate token embeddings.
    Loads the correct class, e.g. BERT / RoBERTa etc.

    :param model_name_or_path: Huggingface models name (https://huggingface.co/models)
    :param max_seq_length: Truncate any inputs longer than max_seq_length
    :param model_args: Arguments (key, value pairs) passed to the Huggingface Transformers model
    :param cache_dir: Cache dir for Huggingface Transformers to store/load models
    :param tokenizer_args: Arguments (key, value pairs) passed to the Huggingface Tokenizer model
    :param do_lower_case: If true, lowercases the input (independent if the model is cased or not)
    :param tokenizer_name_or_path: Name or path of the tokenizer. When None, then model_name_or_path is used
    """
    def __init__(self, model_name_or_path: str, max_seq_length: Optional[int] = None,
                 model_args: Dict = {}, cache_dir: Optional[str] = None,
                 tokenizer_args: Dict = {}, do_lower_case: bool = False,
                 tokenizer_name_or_path : str = None):
        super(Transformer, self).__init__()
        self.config_keys = ['max_seq_length', 'do_lower_case']
        self.do_lower_case = do_lower_case

        config = AutoConfig.from_pretrained(model_name_or_path, **model_args, cache_dir=cache_dir)
        self._load_model(model_name_or_path, config, cache_dir, **model_args)

        self.tokenizer = AutoTokenizer.from_pretrained(tokenizer_name_or_path if tokenizer_name_or_path is not None else model_name_or_path, cache_dir=cache_dir, **tokenizer_args)

        #No max_seq_length set. Try to infer from model
        if max_seq_length is None:
            if hasattr(self.auto_model, "config") and hasattr(self.auto_model.config, "max_position_embeddings") and hasattr(self.tokenizer, "model_max_length"):
                max_seq_length = min(self.auto_model.config.max_position_embeddings, self.tokenizer.model_max_length)

        self.max_seq_length = max_seq_length

        if tokenizer_name_or_path is not None:
            self.auto_model.config.tokenizer_class = self.tokenizer.__class__.__name__


    def _load_model(self, model_name_or_path, config, cache_dir, **model_args):
        """Loads the transformer model"""
        if isinstance(config, T5Config):
            self._load_t5_model(model_name_or_path, config, cache_dir, **model_args)
        elif isinstance(config, MT5Config):
            self._load_mt5_model(model_name_or_path, config, cache_dir, **model_args)
        else:
            self.auto_model = AutoModel.from_pretrained(model_name_or_path, config=config, cache_dir=cache_dir, **model_args)

    def _load_t5_model(self, model_name_or_path, config, cache_dir, **model_args):
        """Loads the encoder model from T5"""
        from transformers import T5EncoderModel
        T5EncoderModel._keys_to_ignore_on_load_unexpected = ["decoder.*"]
        self.auto_model = T5EncoderModel.from_pretrained(model_name_or_path, config=config, cache_dir=cache_dir, **model_args)

    def _load_mt5_model(self, model_name_or_path, config, cache_dir, **model_args):
        """Loads the encoder model from T5"""
        from transformers import MT5EncoderModel
        MT5EncoderModel._keys_to_ignore_on_load_unexpected = ["decoder.*"]
        self.auto_model = MT5EncoderModel.from_pretrained(model_name_or_path, config=config, cache_dir=cache_dir, **model_args)

    def __repr__(self):
        return "Transformer({}) with Transformer model: {} ".format(self.get_config_dict(), self.auto_model.__class__.__name__)

    def forward(self, features):
        """Returns token_embeddings, cls_token"""
        trans_features = {'input_ids': features['input_ids'], 'attention_mask': features['attention_mask']}
        if 'token_type_ids' in features:
            trans_features['token_type_ids'] = features['token_type_ids']

        output_states = self.auto_model(**trans_features, return_dict=False)
        output_tokens = output_states[0]

        features.update({'token_embeddings': output_tokens, 'attention_mask': features['attention_mask']})

        if self.auto_model.config.output_hidden_states:
            all_layer_idx = 2
            if len(output_states) < 3: #Some models only output last_hidden_states and all_hidden_states
                all_layer_idx = 1

            hidden_states = output_states[all_layer_idx]
            features.update({'all_layer_embeddings': hidden_states})

        return features

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

    def tokenize(self, texts: Union[List[str], List[Dict], List[Tuple[str, str]]]):
        """
        Tokenizes a text and maps tokens to token-ids
        """
        output = {}
        if isinstance(texts[0], str):
            to_tokenize = [texts]
        elif isinstance(texts[0], dict):
            to_tokenize = []
            output['text_keys'] = []
            for lookup in texts:
                text_key, text = next(iter(lookup.items()))
                to_tokenize.append(text)
                output['text_keys'].append(text_key)
            to_tokenize = [to_tokenize]
        else:
            batch1, batch2 = [], []
            for text_tuple in texts:
                batch1.append(text_tuple[0])
                batch2.append(text_tuple[1])
            to_tokenize = [batch1, batch2]

        #strip
        to_tokenize = [[str(s).strip() for s in col] for col in to_tokenize]

        #Lowercase
        if self.do_lower_case:
            to_tokenize = [[s.lower() for s in col] for col in to_tokenize]

        output.update(self.tokenizer(*to_tokenize, padding=True, truncation='longest_first', return_tensors="pt", max_length=self.max_seq_length))
        return output


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

    def save(self, output_path: str):
        self.auto_model.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):
        #Old classes used other config names than 'sentence_bert_config.json'
        for config_name in ['sentence_bert_config.json', 'sentence_roberta_config.json', 'sentence_distilbert_config.json', 'sentence_camembert_config.json', 'sentence_albert_config.json', 'sentence_xlm-roberta_config.json', 'sentence_xlnet_config.json']:
            sbert_config_path = os.path.join(input_path, config_name)
            if os.path.exists(sbert_config_path):
                break

        with open(sbert_config_path) as fIn:
            config = json.load(fIn)
        return Transformer(model_name_or_path=input_path, **config)