code: def land(self, velocity=DEFAULT):
          
          if self._is_flying:
              duration_s = self._z / self._velocity(velocity)
              self._hl_commander.land(0, duration_s)
              time.sleep(duration_s)
              self._z = 0.0
  
              self._hl_commander.stop()
              self._is_flying = False
docs: Go straight down and turn off the motors.
  
          Do not call this function if you use the with keyword. Landing is
          done automatically when the context goes out of scope.
  
          :param velocity: The velocity (meters/second) when going down
          :return: