Subscribe and read several topics on mqtt mosquitto using python paho

Question

I managed to publish on several topics and read one of them. What I need to do is to listen and read to all published topics and get messages. This is the code I use:

1. Publish messages to 3 topics :

   #!/usr/bin/env python3
   
   
   import paho.mqtt.client as mqtt
   
   client = mqtt.Client()
   client.connect("localhost",1883,60)
   client.publish("topic/1", "400 | 350 | 320 | 410");
   client.publish("topic/2", "200 | 350 | 420 | 110");
   client.publish("topic/3", "200 | 350 | 420 | 110");
   
   client.disconnect();
   

2. Subscribe and read messages for 1 topic

   #!/usr/bin/env python3
   
   import paho.mqtt.client as mqttClient
   import time
   
   def on_connect(client, userdata, flags, rc):
   
   if rc == 0:
   
       print("Connected to broker")
   
       global Connected                #Use global variable
       Connected = True                #Signal connection 
   
   else:
   
       print("Connection failed")
   
   def on_message(client, userdata, message):
   print "Message received : "  + message.payload
   
   Connected = False   
   
   broker_address= "localhost"          
   port = 1883                          
   
   client = mqttClient.Client("Python")          
   client.on_connect= on_connect    
   client.on_message= on_message        
   client.connect(broker_address, port=port)     
   client.loop_start()        
   
   while Connected != True:   
       time.sleep(0.1)
   
   client.subscribe("topic/2")
   try:
   while True:
       time.sleep(1)
   
   except KeyboardInterrupt:
   print "exiting"
   client.disconnect()
   client.loop_stop()
   

Answer 1

You can call the client.subscribe() function multiple times to subscribe to multiple topics.

Also you should move the calls to subscribe to the on_connect callback to remove the need for the first loop.

#!/usr/bin/env python3

import paho.mqtt.client as mqttClient
import time

def on_connect(client, userdata, flags, rc):
    if rc == 0:
        print("Connected to broker")
        client.subscribe("topic/1")
        client.subscribe("topic/2")
        client.subscribe("topic/3")
        client.subscribe("topic/4")

    else:
        print("Connection failed")

def on_message(client, userdata, message):
    print("Message received : "  + str(message.payload) + " on " + message.topic)


broker_address= "localhost"          
port = 1883                          

client = mqttClient.Client("Python")          
client.on_connect= on_connect    
client.on_message= on_message        
client.connect(broker_address, port=port)     
client.loop_start()


try:
    while True:
        time.sleep(1)

except KeyboardInterrupt:
    print("exiting")
    client.disconnect()
    client.loop_stop()

EDIT:

You can also subscribe to multiple topics in one go with the following syntax

client.subscribe([("topic/1", 0), ("topic/2", 0), ("topic/3", 0),("topic/4", 0)])