code: def clustering_fields(self):
          
          prop = self._properties.get("clustering")
          if prop is not None:
              return list(prop.get("fields", ()))
docs: Union[List[str], None]: Fields defining clustering for the table
  
          (Defaults to :data:`None`).
  
          Clustering fields are immutable after table creation.
  
          .. note::
  
             As of 2018-06-29, clustering fields cannot be set on a table
             which does not also have time partioning defined.