code: def getDataHandler(self, measurementId, deviceId):
          
          am = next((m for m in self.activeMeasurements if m.id == measurementId), None)
          if am is None:
              return None, None
          else:
              device = self.deviceController.getDevice(deviceId)
              if device is None:
                  return None, None
              else:
                  return am, device.dataHandler
docs: finds the handler.
          :param measurementId: the measurement
          :param deviceId: the device.
          :return: active measurement and handler