docs: def _delete_from_indices(self, pipeline):
          """Deletes the object's id from the sets(indices) it has been added
          to and removes its list of indices (used for housekeeping).
          """
          s = Set(self.key()['_indices'])
          z = Set(self.key()['_zindices'])
          for index in s.members:
              pipeline.srem(index, self.id)
          for index in z.members:
              pipeline.zrem(index, self.id)
          pipeline.delete(s.key)
          pipeline.delete(z.key)