浅谈Python之Mqtt

一、基本介绍

在Python中使用MQTT，通常会使用paho-mqtt这个库，它是一个广泛使用的MQTT客户端库，支持MQTT v3.1和v3.1.1协议。

二、基本步骤

安装paho-mqtt库：

使用pip安装paho-mqtt库：

bash 复制代码

pip3 install paho-mqtt

创建MQTT连接：

设置MQTT代理（Broker）的地址、端口和主题（topic），并生成一个随机的客户端ID。

python 复制代码

from paho.mqtt import client as mqtt_client
import random

broker = 'broker.emqx.io'  # MQTT代理地址
port = 1883                # MQTT代理端口
topic = "/python/mqtt"     # 订阅的主题
client_id = f'python-mqtt-{random.randint(0, 1000)}'  # 客户端ID

编写连接回调函数：

当客户端成功连接到MQTT代理时，会调用on_connect回调函数。

python 复制代码

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)

创建客户端并连接：

创建一个MQTT客户端对象，并设置连接回调函数，然后连接到MQTT代理。

python 复制代码

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

发布消息：

使用publish方法向指定的主题发布消息。

python 复制代码

def publish(client):
    msg_count = 0
    while True:
        msg = f"messages: {msg_count}"
        result = client.publish(topic, msg)
        if result[0] == 0:
            print(f"Send `{msg}` to topic `{topic}`")
        else:
            print(f"Failed to send message to topic {topic}")
        msg_count += 1
        time.sleep(1)

订阅消息：

设置on_message回调函数来处理接收到的消息，并使用subscribe方法订阅主题。

python 复制代码

def on_message(client, userdata, msg):
    print(f"Received `{msg.payload.decode()}` from `{msg.topic}` topic")

def subscribe(client):
    client.subscribe(topic)
    client.on_message = on_message

启动网络循环：

使用loop_forever或loop_start方法启动网络循环，以处理网络事件。

python 复制代码

client.loop_forever()  # 或者使用 client.loop_start() 在不同的线程中运行

三、完整代码示例

以下是一个完整的代码示例，展示了如何连接MQTT代理、发布消息和订阅消息。

python 复制代码

# python 3.6
import random
import time
from paho.mqtt import client as mqtt_client

broker = 'broker.emqx.io'
port = 1883
topic = "/python/mqtt"
client_id = f'python-mqtt-{random.randint(0, 1000)}'

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)

def on_message(client, userdata, msg):
    print(f"Received `{msg.payload.decode()}` from `{msg.topic}` topic")

def publish(client):
    msg_count = 0
    while True:
        msg = f"messages: {msg_count}"
        result = client.publish(topic, msg)
        if result[0] == 0:
            print(f"Send `{msg}` to topic `{topic}`")
        else:
            print(f"Failed to send message to topic {topic}")
        msg_count += 1
        time.sleep(1)

def subscribe(client):
    client.subscribe(topic)
    client.on_message = on_message

def run():
    client = mqtt_client.Client(client_id)
    client.on_connect = on_connect
    client.on_message = on_message
    client.connect(broker, port)
    client.loop_start()
    publish(client)

if __name__ == '__main__':
    run()