code: def recalculate(self, parent, updates):
          
          rule_function, children = self._aggregates[parent]
          rule_function(parent, children)
docs: Re-calculate the value of parent sensor.
  
          Parent's value is calculated by calling the associate aggregation rule.
  
          Parameters
          ----------
          parent : :class:`katcp.Sensor` object
              The sensor that needs to be updated.
          updates : sequence of :class:`katcp.Sensor` objects
              The child sensors which triggered the update.