上面的代码如何实现MQTT的断线重连，请给出响应micropython代码

以下是一个基本的MQTT断线重连的Micropython代码示例：

import time
import network
from umqtt.simple import MQTTClient

# MQTT服务器的地址和端口
MQTT_SERVER = "mqtt.server.com"
MQTT_PORT = 1883

# MQTT客户端ID
MQTT_CLIENT_ID = "myclientid"

# MQTT主题
MQTT_TOPIC = "mytopic"

# MQTT用户名和密码
MQTT_USER = "myusername"
MQTT_PASSWORD = "mypassword"

# MQTT客户端实例
mqtt_client = None

# WiFi连接
wifi_ssid = "mywifissid"
wifi_password = "mywifipassword"

def connect_wifi():
    """连接WiFi"""
    wlan = network.WLAN(network.STA_IF)
    wlan.active(True)
    if not wlan.isconnected():
        print("Connecting to WiFi...")
        wlan.connect(wifi_ssid, wifi_password)
        while not wlan.isconnected():
            time.sleep(1)
    print("WiFi connected:", wlan.ifconfig())

def mqtt_callback(topic, msg):
    """MQTT消息回调函数"""
    print(topic, msg)

def connect_mqtt():
    """连接MQTT"""
    global mqtt_client
    mqtt_client = MQTTClient(MQTT_CLIENT_ID, MQTT_SERVER, MQTT_PORT, MQTT_USER, MQTT_PASSWORD)
    mqtt_client.set_callback(mqtt_callback)
    mqtt_client.connect()
    mqtt_client.subscribe(MQTT_TOPIC)

def main():
    """主函数"""
    connect_wifi()  # 连接WiFi
    connect_mqtt()  # 连接MQTT

    while True:
        try:
            mqtt_client.wait_msg()
        except OSError:
            print("MQTT connection lost. Reconnecting...")
            connect_mqtt()

if __name__ == "__main__":
    main()

在这个示例中，我们使用`MQTTClient.wait_msg()`方法来循环等待MQTT消息。如果发生连接丢失错误（`OSError`），则会打印一条消息，并尝试重新连接MQTT服务器。在重新连接之前，我们需要重新创建MQTT客户端实例，并重新订阅我们感兴趣的主题。