Django集成MQTT调用全局变量test报name 'test' is not defined如何解决

• 全局变量未提前初始化：你仅在on_message回调中声明了global test，但没有在模块顶层预先定义该变量。如果showdata被调用时还从未触发过MQTT消息回调，test变量就不存在，直接抛出未定义错误。
• MQTT客户端未实际运行：你写的run()启动逻辑在if __name__ == '__main__'判断下，启动Django服务时（通常用python manage.py runserver）不会执行这段逻辑，MQTT客户端根本没启动，on_message永远不会被触发，test永远不会被赋值。而且client.loop_forever()是阻塞方法，直接在主进程运行会卡住Django的HTTP请求处理逻辑。
• on_message回调参数错误：paho-mqtt的on_message回调的入参是固定的client、userdata、msg三个参数，你自行添加的request参数会导致回调触发时参数不匹配报错，无法完成test变量的赋值。

1. 顶层初始化全局变量
   在文件导入语句下方预先定义test的初始值，避免未定义错误：

test = "暂未收到MQTT数据"

2. 修复on_message的参数错误
   删掉多余的request参数：

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

3. 单独启动MQTT线程避免阻塞Django
   把MQTT客户端逻辑放到守护线程中，在Django启动时自动运行。修改后完整代码如下：

from django.shortcuts import render
from paho.mqtt import client as mqtt_client
import random
import threading


broker = 'localhost'
port = 1883
topic = "Wind"
client_id = f'python-mqtt-{random.randint(0, 100)}'
# 初始化全局变量
test = "暂未收到MQTT数据"


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

    client.subscribe(topic)
    client.on_message = on_message

def run_mqtt():
    client = connect_mqtt()
    subscribe(client)
    client.loop_forever()

# 启动MQTT守护线程，不阻塞Django主进程
mqtt_thread = threading.Thread(target=run_mqtt, daemon=True)
mqtt_thread.start()

def showdata(request):
    context = test
    return render(request, 'index.html', {'data': context})

内容的提问来源于stack exchange，提问作者terry555