code: def recalculate(self, parent, updates):
          
          not_ok = self._parent_to_not_ok[parent]
          children = self.children(parent) if parent in self else set()
          for sensor in updates:
              if sensor not in children or sensor.value():
                  not_ok.discard(sensor)
              else:
                  not_ok.add(sensor)
          parent.set_value(not not_ok)
docs: Re-calculate the value of parent sensor.
  
          Parent's value is the boolean AND of all child sensors.
  
          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.