src/transformers/tokenization_utils.py/PreTrainedTokenizer/__init__
class PreTrainedTokenizer:    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        # Added tokens - We store this for both slow and fast tokenizers
        # until the serialization of Fast tokenizers is updated
        self.added_tokens_encoder: Dict[str, int] = {}
        self.added_tokens_decoder: Dict[int, str] = {}
        self.unique_no_split_tokens: List[str] = []
        self.tokens_trie = Trie()

        self._decode_use_source_tokenizer = False