Paho MQTT client connection reliability (reconnect on disconnection)

Question

What is the most reliable way to use the Python Paho MQTT client? I want to be able to handle connection interruptions due to WiFi drops and keep trying to reconnect until it's successful.

What I have is the following, but are there any best practices I'm not adhering to?

import argparse
from time import sleep

import paho.mqtt.client as mqtt


SUB_TOPICS = ("topic/something", "topic/something_else")
RECONNECT_DELAY_SECS = 2


def on_connect(client, userdata, flags, rc):
    print "Connected with result code %s" % rc
    for topic in SUB_TOPICS:
        client.subscribe(topic)

# EDIT: I've removed this function because the library handles
#       reconnection on its own anyway.
# def on_disconnect(client, userdata, rc):
#     print "Disconnected from MQTT server with code: %s" % rc
#     while rc != 0:
#         sleep(RECONNECT_DELAY_SECS)
#         print "Reconnecting..."
#         rc = client.reconnect()


def on_msg(client, userdata, msg):
    print "%s %s" % (msg.topic, msg.payload)


if __name__ == "__main__":
    p = argparse.ArgumentParser()
    p.add_argument("user")
    p.add_argument("password")
    p.add_argument("host")
    p.add_argument("--port", type=int, default=1883)
    args = p.parse_args()

    client = mqtt.Client()
    client.on_connect = on_connect
    client.on_message = on_msg
    client.username_pw_set(args.user, args.password)
    client.connect(args.host, args.port, 60)
    client.loop_start()

    try:
        while True:
            sleep(1)
    except KeyboardInterrupt:
        pass
    finally:
        client.loop_stop()

Answer 1

1. Set a client_id so it's the same across reconnects
2. Set the clean_session=false connection option
3. Subscribe at QOS greater than 0

These options will help ensure that any messages published while disconnected will be delivered once the connection is restored.

You can set the client_id and clean_session flag in the constructor

client = mqtt.Client(client_id="foo123", clean_session=False)

And set the QOS of the subscription after the topic

client.subscribe(topic, qos=1)