code: def get_metadata(feature_name, etextno):
      
      metadata_values = MetadataExtractor.get(feature_name).get_metadata(etextno)
      return frozenset(metadata_values)
docs: Looks up the value of a meta-data feature for a given text.
  
      Arguments:
          feature_name (str): The name of the meta-data to look up.
          etextno (int): The identifier of the Gutenberg text for which to look
              up the meta-data.
  
      Returns:
          frozenset: The values of the meta-data for the text or an empty set if
              the text does not have meta-data associated with the feature.
  
      Raises:
          UnsupportedFeature: If there is no MetadataExtractor registered that
              can extract meta-data for the given feature name.