The init_mqtt() method

We see the Paho-MQTT client instance created and assigned to the global client variable at line (15). A reference to this object is the  client parameter we saw previously in the on_connect(), on_disconnect(), and on_message() methods.

The client_id parameter is set to be the client name we defined earlier in CLIENT_ID, while clean_session=False tells the broker that it must not clear any stored messages for our client when we connect. As we discussed earlier in the command-line examples, this is the back-to-front way of saying we want a durable connection so any messages published to the led topic are stored for our client when it's offline:

def init_mqtt():
    global client
    client = mqtt.Client(                                       # (15)
        client_id=CLIENT_ID,
        clean_session=False)

    # Route Paho logging to Python logging.
    client.enable_logger()                                      # (16)

    # Setup callbacks
    client.on_connect...