Callback parameters to GPIO.add_event_detect?

Question

I have a button object that when pressed needs to perform something, and for this I'd need to get a property of the button. I'd like it to work like:

...
GPIO.add_event_detect(button, GPIO.RISING, callback=button_callback(button)) #I believe I can't add a parameter to button_callback like this
...

and then

def button_callback(button):
    do_something(button.id)

Is this possible? How can I access the button object from within the callback?

Answer 1

I ran into the same issue. You can solve it without using another library.

This is how you do it.

def button_callback(button):
    print('Button {} pressed'.format(button))

GPIO.add_event_detect(button, GPIO.FALLING, callback=lambda x: button_callback(1))

By using the lambda, you are executing an anonymous function which then calls your button_callback function. Just pass the button id so you know which button was pressed.

Hope this helps! Also, this is my first answer ever on the Stack so please upvote and save as best answer :)

Answer 2

gpzero has support for events, very much what you are looking for event-wise:

from gpiozero import Button

def pushed_17():
    print("Don't push the button!")

b = Button(17)
b.when_pressed = pushed_17

From GPIO perspective the buttons don't really have properties other than the PIN they are assigned to: this way even if you had multiple buttons assigned to the same PIN for some reason, you won't be able to track which one exactly was pressed. Unless you wire them to different PINs or build a small adapter to stay framework agnostic:

def button_push(id):
    #do something based on the id passed
    print("Button {} pressed".format(id))

def push_15():
    return button_push(15)