code: def id_range(self):
          
  
          if len(self._anchor_points) == 0:
              return (0, 0)
  
          return (self._anchor_points[0].reading_id, self._anchor_points[-1].reading_id)
docs: Get the range of archor reading_ids.
  
          Returns:
              (int, int): The lowest and highest reading ids.
  
              If no reading ids have been loaded, (0, 0) is returned.