passing arguments to a callback function in Python

Question

I want to know the syntax for passing arguments to a callback function.

Here is my code :

#!/usr/bin/env python3
import sys,os,time
import RPi.GPIO as GPIO
import subprocess

flag_callback=True

def Callback(channel,port_nb,dist_user,dist_ip):
        global flag_callback
        flag_callback=False
        print('Button Pushed. SSH Tunnel open on port: \"{}\" until reboot.'.format(port_nb))
        bashCommand = "nohup ssh -NR {}:localhost:22 {}@{}".format(port_nb,dist_user,dist_ip)
        subprocess.Popen(bashCommand.split(),
                stdout=open('/dev/null', 'w'),
                stderr=open('logfile.log', 'a'),
                preexec_fn=os.setpgrp
                )

def main():
        if len(sys.argv) > 1:
                port_nb=sys.argv[1]
        else:
                port_nb='2222'

        if len(sys.argv) > 2:
                dist_user=sys.argv[2]
        else:
                dist_user='martin'

        if len(sys.argv) > 3:
                dist_ip = sys.argv[3]
        else:
                dist_ip='192.168.11.111'
        GPIO.setmode(GPIO.BCM)
        GPIO.setup(4, GPIO.IN, pull_up_down=GPIO.PUD_UP)
        GPIO.add_event_detect(4, GPIO.FALLING, callback = Callback(port_nb,dist_user,dist_ip), bouncetime = 1000)
        try:
                while(flag_callback):
                        time.sleep(1)
        except:
                pass

if __name__== "__main__":
  main()

But it's not working... :

Traceback (most recent call last):
  File "./OnPushButton_PULLUP.py", line 55, in <module>
    main()
  File "./OnPushButton_PULLUP.py", line 47, in main
    GPIO.add_event_detect(4, GPIO.FALLING, callback = Callback(port_nb,dist_user,dist_ip), bouncetime = 1000)
TypeError: Callback() missing 1 required positional argument: 'dist_ip'

I missed sth but I don't understand what...I took a look right here but still stuck at this point :/

Does this answer your question? Python, how to pass an argument to a function pointer parameter? — user202729
– user202729, Commented Aug 15, 2021 at 6:36
This question is too dense to be helpful. Use a minimal example. I have this same question but the specifics are too thick. — Mote Zart
– Mote Zart, Commented Aug 4, 2022 at 17:36

Kurtis Rader · Accepted Answer · 2019-07-20 20:41:25Z

10

The usual solution for this scenario is to use functools.partial(). See this article for one explanation with examples: https://www.geeksforgeeks.org/partial-functions-python/

answered Jul 20, 2019 at 20:41

Kurtis Rader

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Julionabi · Accepted Answer · 2019-07-19 11:42:19Z

2

Okay I managed by doing this :

GPIO.add_event_detect(4, GPIO.FALLING, lambda channel,tmp_port=port_nb,tmp_user=dist_user,tmp_ip=dist_ip:Callback(channel,tmp_port,tmp_user,tmp_ip), bouncetime = 1000)

answered Jul 19, 2019 at 11:42

Julionabi

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