src/transformers/models/luke/tokenization_luke.py/LukeTokenizer/__init__
class LukeTokenizer:    def __init__(
        self,
        vocab_file,
        merges_file,
        entity_vocab_file,
        task=None,
        max_entity_length=32,
        max_mention_length=30,
        entity_token_1="<ent>",
        entity_token_2="<ent2>",
        **kwargs
    ):
        # we add 2 special tokens for downstream tasks
        # for more information about lstrip and rstrip, see https://github.com/huggingface/transformers/pull/2778
        entity_token_1 = (
            AddedToken(entity_token_1, lstrip=False, rstrip=False)
            if isinstance(entity_token_1, str)
            else entity_token_1
        )
        entity_token_2 = (
            AddedToken(entity_token_2, lstrip=False, rstrip=False)
            if isinstance(entity_token_2, str)
            else entity_token_2
        )
        kwargs["additional_special_tokens"] = kwargs.get("additional_special_tokens", [])
        kwargs["additional_special_tokens"] += [entity_token_1, entity_token_2]

        super().__init__(
            vocab_file=vocab_file,
            merges_file=merges_file,
            task=task,
            max_entity_length=32,
            max_mention_length=30,
            entity_token_1="<ent>",
            entity_token_2="<ent2>",
            **kwargs,
        )

        with open(entity_vocab_file, encoding="utf-8") as entity_vocab_handle:
            self.entity_vocab = json.load(entity_vocab_handle)

        self.task = task
        if task is None or task == "entity_span_classification":
            self.max_entity_length = max_entity_length
        elif task == "entity_classification":
            self.max_entity_length = 1
        elif task == "entity_pair_classification":
            self.max_entity_length = 2
        else:
            raise ValueError(
                f"Task {task} not supported. Select task from ['entity_classification', 'entity_pair_classification', 'entity_span_classification'] only."
            )

        self.max_mention_length = max_mention_length