src/transformers/models/bert_generation/tokenization_bert_generation.py/BertGenerationTokenizer/__init__
class BertGenerationTokenizer:    def __init__(
        self,
        vocab_file,
        bos_token="<s>",
        eos_token="</s>",
        unk_token="<unk>",
        pad_token="<pad>",
        sep_token="<::::>",
        sp_model_kwargs: Optional[Dict[str, Any]] = None,
        **kwargs
    ) -> None:
        self.sp_model_kwargs = {} if sp_model_kwargs is None else sp_model_kwargs

        # Add extra_ids to the special token list
        super().__init__(
            bos_token=bos_token,
            eos_token=eos_token,
            unk_token=unk_token,
            pad_token=pad_token,
            sep_token=sep_token,
            sp_model_kwargs=self.sp_model_kwargs,
            **kwargs,
        )

        self.vocab_file = vocab_file

        self.sp_model = spm.SentencePieceProcessor(**self.sp_model_kwargs)
        self.sp_model.Load(vocab_file)