Getting 'Nonetype is not callable' error but I don't know why

Question

I'm trying to create a reaction time game thing, however when I press enter after the hotkey is added I get a super long Nonetype error making reference to several different files.

import time
import datetime
import random
import keyboard

playing=True

def stop(playing):
    playing=False

input("Press enter when you're ready to test your reaction time!")
print("Press enter when you see the cat!")

time.sleep(1)

keyboard.add_hotkey('enter', stop(playing))

time.sleep(random.randint(3,6))

if(playing==True):
    keyboard.remove_hotkey('enter')
    start = datetime.datetime.now()
    input("Press Enter!!!!")
    end = datetime.datetime.now()
    print(end-start)

The idea of the hotkey is to stop the user from being able to just hold the enter button down. I don't know why this doesn't work.

I tried adding 'return playing' to the end of the function but that just gave me a similar error of 'bool is not callable'

Answer 1

stop(playing) returns None, so when you do:

keyboard.add_hotkey('enter', stop(playing))

it's exactly as if you did:

stop(playing)
keyboard.add_hotkey('enter', None)

The second argument to add_hotkey is supposed to be a function (not the result of calling a function), so if you pass it None, it raises an error.

What I think you want to do is define your stop function so that it can be called with no arguments, and sets the global playing variable to False:

def stop()
    global playing
    playing = False

and then pass the function (without calling it yet) to add_hotkey:

keyboard.add_hotkey('enter', stop)