code: def previous_calling_points(self):
          
          calling_points = list()
          for cpl in self._previous_calling_point_lists:
              calling_points += cpl.calling_points
          return calling_points
docs: A list of CallingPoint objects.
  
          This is the list of all previous calling points for the service,
          including all associated services if multiple services join together
          to form this service.