code: def list_completeness_index(self, start=None, stop=None):
          
          params = {}
          if start is not None:
              params['start'] = to_isostring(start)
          if stop is not None:
              params['stop'] = to_isostring(stop)
  
          return pagination.Iterator(
              client=self._client,
              path='/archive/{}/completeness-index'.format(self._instance),
              params=params,
              response_class=archive_pb2.IndexResponse,
              items_key='group',
              item_mapper=IndexGroup,
          )
docs: Reads completeness index records between the specified start and stop
          time.
  
          Each iteration returns a chunk of chronologically-sorted records.
  
          :rtype: ~collections.Iterable[.IndexGroup]