class LaserDistance(ReadonlyRegisterBase):
    def __init__(self):
        ReadonlyRegisterBase.__init__(self, "laser_distance")
    def doRead(self):
        ret = ue.readable.read()
        ret = 0.0 if math.isnan(ret) else ret
        return ret

class ListenerAI (DeviceListener):
    def onValueChanged(self, device, value, former):
        laser_distance.setCache( 0.0 if math.isnan(value) else value, None)

listenerAI = ListenerAI()
ue.addListener(listenerAI)
        
laser_distance=LaserDistance()   
add_device(laser_distance, True)