src/transformers/tokenization_utils_base.py/PreTrainedTokenizerBase/save_vocabulary
class PreTrainedTokenizerBase:    def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
        """
        Save only the vocabulary of the tokenizer (vocabulary + added tokens).

        This method won't save the configuration and special token mappings of the tokenizer. Use
        [`~PreTrainedTokenizerFast._save_pretrained`] to save the whole state of the tokenizer.

        Args:
            save_directory (`str`):
                The directory in which to save the vocabulary.
            filename_prefix (`str`, *optional*):
                An optional prefix to add to the named of the saved files.

        Returns:
            `Tuple(str)`: Paths to the files saved.
        """
        raise NotImplementedError