def __getitem__(self, item: str) -> Union[Any]:
        """
        If the key is a string, returns the value of the dict associated to `key` ('input_values', 'attention_mask',
        etc.).
        """
        if isinstance(item, str):
            return self.data[item]
        else:
            raise KeyError("Indexing with integers is not available when using Python based feature extractors")

        If the key is a string, returns the value of the dict associated to `key` ('input_values', 'attention_mask',
        etc.).
        
dpkd/transformers/src/transformers/feature_extraction_utils.py