Retained messages in IOT Protocols - Mini Project: Build & Apply

Understanding Retained Messages in MQTT

📖 Scenario: You are working with MQTT, a messaging protocol used in IoT devices. Retained messages help new subscribers get the last known message immediately after subscribing.Imagine you have a smart home system where sensors send temperature updates. You want new devices to get the latest temperature right away without waiting for the next update.

🎯 Goal: Build a simple simulation of MQTT retained messages using a Python dictionary. You will store messages with a retained flag, update the retained messages, and retrieve the last retained message for a topic.

📋 What You'll Learn

Create a dictionary to store MQTT topics and their retained messages

Add a variable to represent a new message with a retained flag

Write logic to update the retained message only if the retained flag is true

Print the retained message for a specific topic

💡 Why This Matters

🌍 Real World

MQTT retained messages are used in IoT devices to ensure new subscribers get the latest state immediately, such as the last temperature reading or device status.

💼 Career

Understanding retained messages is important for IoT developers and DevOps engineers managing MQTT brokers and device communication to ensure reliable and efficient data delivery.

1

Create the initial retained messages dictionary

Create a dictionary called retained_messages with these exact entries: 'home/temperature': '22C', 'home/humidity': '45%'

IOT Protocols

# Create the retained_messages dictionary with initial topics and messages
# Your code here

Need a hint?

Use curly braces to create a dictionary with keys as topic strings and values as message strings.

2

Add a new MQTT message with retained flag

Create a variable called new_message as a dictionary with keys 'topic', 'payload', and 'retained'. Set 'topic' to 'home/temperature', 'payload' to '23C', and 'retained' to true.

IOT Protocols

retained_messages = {'home/temperature': '22C', 'home/humidity': '45%'}
# Create the new_message dictionary with topic, payload, and retained flag
# Your code here

Need a hint?

Create a dictionary with the exact keys and values as specified.

3

Update retained messages if retained flag is true

Write an if statement that checks if new_message['retained'] is true. If yes, update retained_messages for the key new_message['topic'] with the value new_message['payload'].

IOT Protocols

retained_messages = {'home/temperature': '22C', 'home/humidity': '45%'}
new_message = {'topic': 'home/temperature', 'payload': '23C', 'retained': true}
# Update retained_messages if new_message['retained'] is true
# Your code here

Need a hint?

Use an if statement to check the retained flag and update the dictionary accordingly.

4

Print the retained message for 'home/temperature'

Write a print statement to display the retained message for the topic 'home/temperature' from the retained_messages dictionary.

IOT Protocols

retained_messages = {'home/temperature': '22C', 'home/humidity': '45%'}
new_message = {'topic': 'home/temperature', 'payload': '23C', 'retained': true}
if new_message['retained']:
    retained_messages[new_message['topic']] = new_message['payload']
# Print the retained message for 'home/temperature'
# Your code here

Need a hint?

Use print() with the dictionary key to show the updated retained message.