How to fix Python argument error

Question

I have a little python script I got from here. It listens for MQTT messages and plays a .wav file when a topic is published to. However, I get this error when the script is run:

TypeError: on_connect() takes exactly 3 arguments (4 given)

Where is the above error coming from? More importantly, how can I fix it?

Here's my full code:

import paho.mqtt.client as MQTT
# Don't forget to change the variables for the MQTT broker!
mqtt_topic = "button"
mqtt_broker_ip = "192.168.0.55"
song_path = '/home/pi/alerts/buzzer_alert.wav'
# change it to desire duration in seconds
duration_time = 5
client = mqtt.Client()
# These functions handle what happens when the MQTT client connects
# to the broker, and what happens then the topic receives a message
def on_connect(client, userdata, rc):
 # rc is the error code returned when connecting to the broker
 print "Connected!", str(rc)
 # Once the client has connected to the broker, subscribe to the topic
 client.subscribe(mqtt_topic)
def on_message(client, userdata, msg):
 # This function is called everytime the topic is published to.
 # If you want to check each message, and do something depending on
 # the content, the code to do this should be run in this function
 print "Topic: ", msg.topic + "\nMessage: " + str(msg.payload)
 # The message itself is stored in the msg variable
 # and details about who sent it are stored in userdata
 os.system('aplay -d {} {}'.format(duration_time, song_path))
# Here, we are telling the client which functions are to be run
# on connecting, and on receiving a message
client.on_connect = on_connect
client.on_message = on_message
# Once everything has been set up, we can (finally) connect to the broker
# 1883 is the listener port that the MQTT broker is using
client.connect(mqtt_broker_ip, 1883)
# Once we have told the client to connect, let the client object run itself
client.loop_forever()
client.disconnect()

• Aurora0001: When you get the error, you should see multiple lines of output (a 'stack trace'). This will help you figure out which line is causing the problem; you should include it here to get help. Also, did you paste part of your code twice? It appears that some of it might have been repeated in your code.
• Allen Jakpa: Ok, I accidentally pasted it twice.

Answer 1

change your on_connect callback to this definition:

def on_connect(client, userdata, flags, rc):
 # rc is the error code returned when connecting to the broker
 print "Connected!", str(rc)
 # Once the client has connected to the broker, subscribe to the topic
 client.subscribe(mqtt_topic)

as mentioned in the paho documentation:

@on_connect.setter
 def on_connect(self, func):
 """ Define the connect callback implementation.
 Expected signature is:
 connect_callback(client, userdata, flags, rc)
 client: the client instance for this callback
 userdata: the private user data as set in Client() or userdata_set()
 flags: response flags sent by the broker
 rc: the connection result

• Allen Jakpa: Awesome! now working. I appreciate your prompt help.
• Allen Jakpa: One more issue though. The wave file is played at the start of the script, not at the press of the button.
• bierschi: Everytime a msg is published to this topic the on_message callback is called. So you have to ensure why is this callback were called at the beginning of your script. I dont know the esp programs. Make some further investigations