如何通过在 Tkinter (Python) 中制作正确的“停止”按钮来中断线程/进程？

Question

I want some basics on the problem of making some sort of "Stop" button that in my case terminates the series of beeps:

from tkinter import *
import winsound
from random import randint

class App(Frame):
    def __init__(self, master=None):
        Frame.__init__(self, master)
        self.pack()
        self.widgets()

    def widgets(self):
        self.beep = Button(self, text = "Beep", command = play_beep)
        self.beep.pack()
        self.stop = Button(self, text = "Stop", command = stop_beep)
        self.stop.pack()

go_on = True
def play_beep():
    count = 10
    while go_on == True and count != 0:
        winsound.Beep(randint(100, 2500), 200)
        count -= 1

def stop_beep():
    go_on = False

root = Tk()
app = App(root)
root.mainloop()

When I press the "Beep" button it gets stuck as well as all the GUI until the beeps end. Could anyone tell me how to fix it?

Answer 1

First off, your question has nothing to do about threads or processes. Tkinter is single-threaded.

If you want to run some function periodically in a tkinter program, you must give the event loop a chance to process events. The typical solution is to do it like this:

def play_beep(count=10):
    if go_on and count != 0:
        winsound.Beep(randint(100, 2500), 200)
        root.after(1000, play_beep, count=1)

This will cause the beep to play every second (1000ms) for ten iterations. In between each call, the event loop will have a chance to process other events.

Now, if the code you are running takes a long time, you're going to have to run that code in a separate thread or process. I know nothing about winsound.Beep so I don't know if that's necessary or not.

Second, to be able to interrupt it, you need to make go_on global, otherwise you're simply setting a local variable that never gets used.

def stop_beek():
    global go_on
    go_on = False

Answer 2

I don't use TKinter, but I believe your button press is not creating a separate thread or process. The reason why your button gets stuck is because your play_beep loop is blocking your GUI execution loop. So we use threading. The thread executes at the same time as your GUI, so you can basically do two things at once (listen for GUI events and play beep noises).

import threading

class App(Frame):
    def __init__(self, master=None):
        Frame.__init__(self, master)
        self.is_playing = False
        self.pack()
        self.widgets()

    def widgets(self):
        self.beep = Button(self, text = "Beep", command = self.play_beep)
        self.beep.pack()
        self.stop = Button(self, text = "Stop", command = self.stop_beep)
        self.stop.pack()

    def play_beep(self):
        self.is_running = True
        self.beep_th = threading.Thread(target=self.run)
        self.beep_th.start()

    def run(self):
        count = 10
        while self.is_running == True and count != 0:
            winsound.Beep(randint(100, 2500), 200)
            count -= 1

    def stop_beep(self):
        try:
            self.is_running = False
            self.beep_th.join(0)
            self.beep_th = None
        except (AttributeError, RuntimeError): # beep thread could be None
            pass

    def closeEvent(self, event): # This is a pyside method look for a TKinter equivalent.
        """When you close the App clean up the thread and close the thread properly."""
        self.stop_beep()
        super().closeEvent(event)