Using the retained message flag in MQTT with Python

import paho.mqtt.client as mqtt

def on_connect(client, userdata, flags, rc):
    print(f"Connected with result code {rc}")
    # Subscribe to a topic and check retained flag
    client.subscribe("test/retained")
    print("Subscribed to test/retained")

def on_message(client, userdata, msg):
    # msg.retain is the MQTT retained flag (True if retained, False if normal)
    print(f"Topic: {msg.topic}")
    print(f"Payload: {msg.payload.decode()}")
    print(f"Retained flag: {msg.retain}")
    print("-" * 30)

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("test.mosquitto.org", 1883, 60)
client.loop_start()

# Publish a normal message (retained=False)
client.publish("test/retained", "normal message", retain=False)

# Publish a retained message (retained=True)
client.publish("test/retained", "retained message", retain=True)

import time
time.sleep(2)
client.loop_stop()
client.disconnect()