[Solved] What will the following code print when a message is received on topic 'test/topic'? import paho.mqtt.... What will the following code print when a message is received on topic 'test/topic'? | Raspberry Pi

Raspberry Pi - MQTT for IoT

What will the following code print when a message is received on topic 'test/topic'?

import paho.mqtt.client as mqtt

def on_message(client, userdata, msg):
    print(f"Received '{msg.payload.decode()}' on topic '{msg.topic}'")

client = mqtt.Client()
client.on_message = on_message
client.connect('broker.hivemq.com', 1883)
client.subscribe('test/topic')
client.loop_start()

# Assume a message with payload 'Hello' is published to 'test/topic'

AReceived b'Hello' on topic 'test/topic'

BReceived 'Hello' on topic 'test/topic'

CReceived 'Hello' on topic 'broker.hivemq.com'

DNo output because loop_start() is missing

Step-by-Step Solution

Solution:

Step 1: Understand on_message callback
The callback decodes the message payload bytes to string and prints it with the topic.
Step 2: Check code behavior on receiving 'Hello'
The payload 'Hello' is decoded and printed with the subscribed topic 'test/topic'.
Final Answer:
Received 'Hello' on topic 'test/topic' -> Option B
Quick Check:
Decoded payload + topic = Received 'Hello' on topic 'test/topic' [OK]

Quick Trick: Decode payload bytes to string before printing [OK]

Common Mistakes:

MISTAKES

Printing raw bytes without decoding
Confusing topic with broker address
Forgetting to start the loop

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What will the following code print when a message is received on topic 'test/topic'?

Step 1: Understand on_message callback

Step 2: Check code behavior on receiving 'Hello'

Final Answer:

Quick Check:

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