code: def mapping(self):
          
  
          return (
              self._user_id_mapping,
              self._user_feature_mapping,
              self._item_id_mapping,
              self._item_feature_mapping,
          )
docs: Return the constructed mappings.
  
          Invert these to map internal indices to external ids.
  
          Returns
          -------
  
          (user id map, user feature map, item id map, item id map): tuple of dictionaries