code: def set_fan_mode(self, mode):
          
          desired_state = {"fan_mode": mode}
  
          response = self.api_interface.set_device_state(self, {
              "desired_state": desired_state
          })
  
          self._update_state_from_response(response)
docs: :param mode: a string one of ["on", "auto"]
          :return: nothing