code: def set_target(self, new_target):
          
          try:
              self.device.target = new_target
              return 'T={}'.format(new_target)
          except RuntimeError:
              return 'err: not idle'
          except ValueError:
              return 'err: not 0<=T<=250'
docs: Sets the new target in mm, the movement starts immediately. If the value is outside
          the interval [0, 250] or the motor is already moving, an error is returned, otherwise
          the new target is returned.