in pysimplegui, simplifying event loop by calling an event handler function

Question

I wanted to simplify the event loop by providing a function to call when the element would generate an event. This works because the 'key' of the elements can also be an object, in this case a newly created Event object. I provide an event handler function to be called, and the idea was that this was called with the value returned by the win.read().

This is my simple example:

import PySimpleGUI as sg

class Event:
    def __init__(self, func):
        self.handler = func

def inputHandler(value):
    print (f"received {value}") 

def buttonHandler(button):
    print ('button was pressed')

def checkBoxHandler(checkbox):
    print (f'check was set {checkbox}')


input = sg.Input('Hello', enable_events = True, readonly=False, key = Event(inputHandler))
check = sg.Checkbox('check this', enable_events = True, key = Event(checkBoxHandler))
button = sg.Button('a button', key = Event(buttonHandler))

# note: elements above can also simply be inserted in layout below

layout = [
    [input],
    [check],
    [button],
]

win = sg.Window('testing function calls as events', layout)

while (True):
    event, values = win.read()
    if event == sg.WIN_CLOSED: 
        break

    event.handler(values[event])

win.close()

This works as expected for the input and the checkbox. When pressing the button it bombs out with a KeyError on the values[].

I guess the button is not present in values[...] so a simple

if event in values:
    ...

might work (did not test)

But:

1. would anybody think of something to make it universal?
2. unrelated to the event loop, why would the values[buttonkey] not contain the pressed/released state?