pythonmqtt 退订

Python MQTT退订是指客户端取消订阅主题，不再接收该主题的消息。在paho-mqtt库中，可以使用`unsubscribe()`方法来实现退订。具体实现步骤如下：
1. 创建一个MQTT客户端对象。
2. 连接MQTT代理服务器。
3. 使用`unsubscribe()`方法取消订阅指定主题。
4. 断开MQTT客户端与代理服务器的连接。

下面是一个简单的Python MQTT退订的示例代码：

import random
from paho.mqtt import client as mqtt_client

broker = 'broker.emqx.io'
port = 1883
topic = "/python/mqtt"

# generate client ID with pub prefix randomly
client_id = f'python-mqtt-{random.randint(0, 100)}'

def connect_mqtt() -> mqtt_client:
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            print("Connected to MQTT Broker!")
        else:
            print("Failed to connect, return code %d\n", rc)

    client = mqtt_client.Client(client_id)
    client.on_connect = on_connect
    client.connect(broker, port)
    return client

def unsubscribe(client: mqtt_client):
    client.unsubscribe(topic)

def run():
    client = connect_mqtt()
    client.loop_start()
    unsubscribe(client)
    client.disconnect()

if __name__ == '__main__':
    run()