    def _get_mapping(
        cls,
        mapping: Optional[Dict[str, str]] = None,
    ):
        """
        Returns the mapping to be used, based on the optional `mapping` overrides
        and the default module-level mapping.
        """
        combined_mapping = {}
        combined_mapping.update(cls._pretrained_mapping)
        if mapping is not None:
            combined_mapping.update(mapping)
        return combined_mapping
Returns the mapping to be used, based on the optional `mapping` overrides
and the default module-level mapping.
allennlp/modules/transformer/transformer_module.py