为什么我无法在Paho MQTT中接收消息？

Question

So I have created this code to send and receive messages using Paho MQTT. It takes input from the user and publishes to a given topic and for taking the input I have created a while loop which will break if the input is 'exit'.

The problem is that I can send messages to the topic but I can't receive them. I only receive them when I give 'exit' as input.

I tried reading the documentation but it was no help, plus I am new to python so maybe its something that I am missing out

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)

EDIT 1: Platforms: Eclipse Paho ver 1.4 OS: Windows 7

Answer 1

Try changing your print calls to include flush=True .

eg

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