MQTT client with Python (paho-mqtt) in IOT Protocols - Mini Project: Build & Apply

MQTT client with Python (paho-mqtt)

📖 Scenario: You want to create a simple program that connects to an MQTT broker and listens for messages on a specific topic. MQTT is a messaging protocol often used in IoT devices to send data efficiently.Imagine you have a smart home sensor that sends temperature updates. Your program will subscribe to these updates and print them out.

🎯 Goal: Build a Python MQTT client using the paho-mqtt library that connects to a broker, subscribes to a topic, and prints received messages.

📋 What You'll Learn

Use the paho.mqtt.client library

Connect to the broker at test.mosquitto.org on port 1883

Subscribe to the topic home/sensor/temperature

Print any message received on that topic

💡 Why This Matters

🌍 Real World

MQTT is widely used in IoT devices like sensors, smart home gadgets, and industrial equipment to send data efficiently over networks.

💼 Career

Understanding how to build MQTT clients is useful for roles in IoT development, DevOps for IoT infrastructure, and automation engineers working with device communication.

1

Setup MQTT client and connect to broker

Import the paho.mqtt.client module as mqtt. Create a client object called client using mqtt.Client(). Connect client to the broker at test.mosquitto.org on port 1883 using client.connect().

IOT Protocols

# Import paho.mqtt.client as mqtt
# Create client with mqtt.Client()
# Connect client to 'test.mosquitto.org' on port 1883
# Your code here

Need a hint?

Use import paho.mqtt.client as mqtt to import the library. Then create the client with mqtt.Client(). Use client.connect() with the broker address and port.

2

Subscribe to the temperature topic

Use the client.subscribe() method to subscribe to the topic 'home/sensor/temperature'.

IOT Protocols

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect('test.mosquitto.org', 1883)
# Subscribe to 'home/sensor/temperature' topic
# Your code here

Need a hint?

Call client.subscribe() with the exact topic string 'home/sensor/temperature'.

3

Define a message callback to print received messages

Define a function called on_message that takes parameters client, userdata, and msg. Inside the function, print the topic and message payload decoded as UTF-8. Assign this function to client.on_message.

IOT Protocols

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect('test.mosquitto.org', 1883)
client.subscribe('home/sensor/temperature')
# Define on_message callback function
# Assign it to client.on_message
# Your code here

Need a hint?

The callback function on_message receives the message object msg. Use msg.topic and msg.payload.decode('utf-8') to get the topic and message text.

4

Start the MQTT client loop to listen for messages

Call client.loop_forever() to start the network loop and keep the client listening for messages indefinitely.

IOT Protocols

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect('test.mosquitto.org', 1883)
client.subscribe('home/sensor/temperature')

def on_message(client, userdata, msg):
    print(f"Received message on topic {msg.topic}: {msg.payload.decode('utf-8')}")

client.on_message = on_message
# Start the MQTT client loop
# Your code here

Need a hint?

Use client.loop_forever() to keep the client running and listening for messages.