src/transformers/models/transfo_xl/tokenization_transfo_xl.py/TransfoXLTokenizer/save_vocabulary
class TransfoXLTokenizer:    def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
        if os.path.isdir(save_directory):
            vocab_file = os.path.join(
                save_directory,
                (filename_prefix + "-" if filename_prefix else "") + VOCAB_FILES_NAMES["pretrained_vocab_file"],
            )
        else:
            vocab_file = (filename_prefix + "-" if filename_prefix else "") + save_directory
        with open(vocab_file, "wb") as f:
            pickle.dump(self.__dict__, f)
        return (vocab_file,)