esp32测试mqtt

import network,time,os
import usocket as socket  # 引用socket模块
from machine import UART
import select,json
from umqtt.simple import MQTTClient
def sub_cb(topic, msg):
        global statemqtt
        print((topic, msg))   #打印收到信息
        if msg == b"on":
            lcdmain.my_text_out("mqtt"+":on",0,32)#单片机显示接收的信息
            statemqtt = 1
        elif msg == b"off":
            lcdmain.my_text_out("mqtt"+":off",0,32)
            statemqtt = 0
        elif msg == b"toggle":
            # LED is inversed, so setting it to current state
            # value will make it toggle
            lcdmain.my_text_out("mqtt"+":tog",0,32)
            statemqtt = 1 - statemqtt
def main():
    c = MQTTClient("umqtt_client", "1.tcp.vip.cpolar.cn",20257)
     #建立一个MQTT客户端
    c.set_callback(sub_cb) #设置回调函数
    c.connect() #建立连接
    c.subscribe(b"mqtt/mypi") #监控ledctl这个通道，接收控制命令

if __name__ == '__main__':
    while True:
      main()