Wildcard subscriptions (+ and #) in IOT Protocols - Mini Project: Build & Apply

Wildcard Subscriptions (+ and #) in MQTT Topics

📖 Scenario: You are setting up an MQTT client to subscribe to sensor data topics. MQTT topics use slashes to separate levels, like home/kitchen/temperature. You want to use wildcards to subscribe to multiple topics easily.The + wildcard matches exactly one level, and the # wildcard matches all remaining levels.

🎯 Goal: Learn how to create MQTT topic subscriptions using the + and # wildcards to receive messages from multiple topics efficiently.

📋 What You'll Learn

Create a list of MQTT topics to subscribe to

Add wildcard subscription patterns using + and #

Filter topics matching the wildcard subscriptions

Print the matched topics

💡 Why This Matters

🌍 Real World

MQTT is widely used in IoT devices to send sensor data. Wildcard subscriptions let you listen to many related topics easily, saving network and processing resources.

💼 Career

Understanding MQTT wildcards is important for IoT developers, DevOps engineers managing IoT infrastructure, and anyone working with message brokers and real-time data streams.

1

Create a list of MQTT topics

Create a list called topics with these exact MQTT topic strings: 'home/kitchen/temperature', 'home/kitchen/humidity', 'home/livingroom/temperature', 'office/room1/temperature', 'office/room2/humidity'.

IOT Protocols

# Create the list called topics with the exact MQTT topic strings
# Your code here

Need a hint?

Use square brackets to create a list and include all topics as strings separated by commas.

2

Add wildcard subscription patterns

Create a list called subscriptions with these exact wildcard subscription strings: 'home/+/temperature' and 'office/#'.

IOT Protocols

topics = ['home/kitchen/temperature', 'home/kitchen/humidity', 'home/livingroom/temperature', 'office/room1/temperature', 'office/room2/humidity']
# Create the list called subscriptions with the exact wildcard strings
# Your code here

Need a hint?

Use a list with the two wildcard subscription strings exactly as shown.

3

Filter topics matching the wildcard subscriptions

Create a function called match_topic that takes subscription and topic strings and returns True if the topic matches the subscription using MQTT wildcard rules for + and #. Then create a list called matched_topics that includes topics from topics matching any subscription in subscriptions.

IOT Protocols

topics = ['home/kitchen/temperature', 'home/kitchen/humidity', 'home/livingroom/temperature', 'office/room1/temperature', 'office/room2/humidity']
subscriptions = ['home/+/temperature', 'office/#']
# Define match_topic(subscription, topic) function
# Create matched_topics list with topics matching any subscription
# Your code here

Need a hint?

Split both subscription and topic by '/' and compare each level. The '+' wildcard matches one level, '#' matches all remaining levels.

4

Print the matched topics

Write a print statement to display the matched_topics list.

IOT Protocols

topics = ['home/kitchen/temperature', 'home/kitchen/humidity', 'home/livingroom/temperature', 'office/room1/temperature', 'office/room2/humidity']
subscriptions = ['home/+/temperature', 'office/#']

def match_topic(subscription, topic):
    sub_levels = subscription.split('/')
    topic_levels = topic.split('/')
    for i, sub_level in enumerate(sub_levels):
        if sub_level == '#':
            return True
        if i >= len(topic_levels):
            return False
        if sub_level != '+' and sub_level != topic_levels[i]:
            return False
    return len(topic_levels) == len(sub_levels)

matched_topics = [topic for topic in topics if any(match_topic(sub, topic) for sub in subscriptions)]
# Print the matched_topics list
# Your code here

Need a hint?

Use print(matched_topics) to show the list of matched topics.