为什么我无法在 Paho MQTT 中接收消息？

Question

所以我创建了这个代码来使用 Paho MQTT 发送和接收消息。它从用户那里获取输入并发布到给定的主题，为了获取输入，我创建了一个 while 循环，如果输入是“退出”，它将中断。

问题是我可以向主题发送消息但我无法接收它们。 我只有在输入“退出”时才会收到它们。

我尝试阅读文档，但没有任何帮助，而且我是 python 新手，所以也许我错过了一些东西

import paho.mqtt.client as mqtt
import os
from urllib.parse import urlparse

# Define event callbacks
def on_connect(client, userdata, flags, rc):
    print("rc: " + str(rc))

def on_message(client, obj, msg):
    print(msg.topic + " " + str(msg.qos) + " " + str(msg.payload))

def on_publish(client, obj, mid):
    print("mid: " + str(mid))

def on_subscribe(client, obj, mid, granted_qos):
    print("Subscribed: " + str(mid) + " " + str(granted_qos))

def on_log(client, obj, level, string):
    print(string)


mqttc = mqtt.Client(client_id="NV")
# Assign event callbacks
mqttc.on_message = on_message
mqttc.on_connect = on_connect
mqttc.on_publish = on_publish
mqttc.on_subscribe = on_subscribe

# Uncomment to enable debug messages
#mqttc.on_log = on_log

topic = 'test'

# Connect
mqttc.username_pw_set(username, pass)
mqttc.connect(server,port)
mqttc.loop_start()
# Start subscribe, with QoS level 0
mqttc.subscribe(topic, 0)

# Publish a specififc message
mqttc.publish(topic,'NV Online')


# INPUT from User
msg = 'run'
while(msg!='exit'):
    msg = input()
    mqttc.publish(topic,msg)

编辑 1： 平台： Eclipse Paho 版本 1.4 操作系统：Windows 7

Answer 1

尝试更改您的 print 调用以包含 flush=True。

例如

def on_message(client, obj, msg):
  print(msg.topic + " " + str(msg.qos) + " " + str(msg.payload), flush=True)