src/transformers/feature_extraction_utils.py/FeatureExtractionMixin/to_json_string
class FeatureExtractionMixin:    def to_json_string(self) -> str:
        """
        Serializes this instance to a JSON string.

        Returns:
            :obj:`str`: String containing all the attributes that make up this feature_extractor instance in JSON
            format.
        """
        return json.dumps(self.to_dict(), indent=2, sort_keys=True) + "\n"