Paho MQTT Python客户端:没有引发异常，只是停止 [英] Paho MQTT Python Client: No exceptions thrown, just stops

问题描述

我尝试在python3中设置一个mqtt客户端.这不是我第一次这样做，但是我遇到了一个很奇怪的行为. 尝试从其中一个回调函数(on_connect或on_message)调用包含错误的函数时，python不会引发异常(至少不打印异常)，而只是在此停止.我把一个简短的例子绑在一起，重现了这种行为.

I try to setup a mqtt client in python3. This is not the first time im doing this, however i came across a rather odd behaviour. When trying to call a function, which contains a bug, from one of the callback functions (on_connect or on_message), python does not throw an exception (at least it is not printed), it just stops there. I tied together a short example, that reproduces that behaviour.

有人有主意吗?

import paho.mqtt.client as mqtt

import re
import os.path

import json
from termcolor import colored

client = mqtt.Client()

def func():
    test = 1 + "1"
    print("Should never reach that")

def on_connect(client, userdata, flags, rc):
    """Establishes connection to broker
    """
    print("Connected to broker with result code " + str(rc))
    client.subscribe("test")

def on_message(client,userdata,msg):
    print("Recieved message on " + msg.topic)
    params = {}
    if msg.topic == "test":

        print("Invoke func")
        func()

if __name__ == "__main__":
    client.on_connect = on_connect
    client.on_message = on_message

    client.connect("localhost",1883,60)

    client.loop_forever()

这是向主题"test"发送消息时的输出:

This is the output when sending a message to the topic "test":

Connected to broker with result code 0
Recieved message on test
Invoke func

当从main调用func()时，我抛出了正确的TypeError.所以有些东西在paho中捕获了此异常.我看了一个较旧的项目(虽然是python2)，并试图重新创建该行为.在那里正确地抛出了异常.我想念什么?

When calling func() from main, i get the correct TypeError thrown. So something catches this exception in paho. I had a look at an olderproject (python2 though) and tried to recreate the behaviour. There the exception gets thrown correctly. What do i miss?

编辑 我可以通过将func()调用放在try块中来捕获异常.但是，如果未被捕获，它不会停止程序的执行.我不明白为什么

EDIT I can catch the exception by putting the func() call in a try block. How ever, it does not stop the execution of the program when not catched. I dont get why

推荐答案

这是由于on_message函数是由网络线程调用的事实，它将把该调用包装在try块中，以阻止on_message中的错误停止该线程.

This will be due to the fact that the on_message function is called by the network thread and it will be wrapping that call in a try block to stop errors in on_message from stopping that thread.

如果您想出错以停止应用程序，则应在on_message中使用您自己的try块并采取适当的措施.

If you want to an error to stop the app then you should use your own try block in on_message and behave appropriately.

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