(Python Kivy) Indexing Which Button Was Pressed

Question

I am trying to figure out a way to index which button was pressed in a GridLayout so that, for instance, I can put a specific image in that button's background when it is pressed. Here is what I am currently doing, using a function just to try to print the index number as a test before adding more functionality:

    for x in range(15):
        self.buttons.append(Button())
        self.ids.grid_1.add_widget(self.buttons[x])
        self.buttons[x].background_normal = 'YOUTUBE.png'
        self.buttons[x].background_down = 'opacity.png'

        # Make the button switch screens to input from calling the function above
        if edit_mode is True:
            self.buttons[x].bind(on_release=self.SwitchScreenInput)
            self.buttons[x].bind(on_release=self.HoldButtonNum(x))

def HoldButtonNum(x):
    print(x)

Im getting the error:

TypeError: HoldButtonNum() takes 1 positional argument but 2 were given

Process finished with exit code 1

Answer 1

I will make some observations:

• If HoldButtonNum is an instance method its first parameter must be self.
• You must use functools.partial or lambda functions to pass arguments to event handler.
• The function must receive a third parameter which is the instance of the button that launches the event.

An example:

from kivy.app import App
from kivy.uix.gridlayout import GridLayout
from kivy.uix.button import Button

from functools import partial
class MyGridLayout(GridLayout):
    cols = 5
    def __init__(self):
        super(MyGridLayout, self).__init__()
        self.buttons = []
        for x in range(15):
            self.buttons.append(Button())
            self.add_widget(self.buttons[x])
            self.buttons[x].bind(on_release=partial(self.HoldButtonNum,  x))

    def HoldButtonNum(self, x, instance):
        print('Button instance:',  instance)
        print('Button index in list:',  x)


class MyKivyApp(App):
    def build(self):
        return MyGridLayout()

def main():
    app = MyKivyApp()
    app.run()

if __name__ == '__main__':
    main()

When a button is pressed the output is like:

Button index in list: 1    
Button instance: <kivy.uix.button.Button object at 0x0000018C511FC798>