CODEWITHSUNDEEP
pythonloopstkinter
Anthony
Anthony

Reputation: 155

Python tkinter start and stop loop?

Ive been trying to make a program with 2 buttons, pressing one of them will start an infinite loop and pressing the other one will stop it.

All the methods ive tried will just pause the loop.

from Tkinter import *
import time
s = 0

def stopit():
    s = 1
    print "stoped"
#
def callback():

    if s == 0:
        while True:
            print "called the callback!"
            time.sleep(3)
            if s == 1:
                break
            #
        #
    #
#

root = Tk()

def main():


    # create a menu
    menu = Menu(root)
    root.config(menu=menu)

    b = Button(root, command=stopit)
    b.pack()


    filemenu = Menu(menu)
    menu.add_cascade(label="File", menu=filemenu)
    filemenu.add_command(label="New", command=callback)
    filemenu.add_command(label="Open...", command=callback)
    filemenu.add_separator()
    filemenu.add_command(label="Exit", command=callback)

    helpmenu = Menu(menu)
    menu.add_cascade(label="Help", menu=helpmenu)
    helpmenu.add_command(label="About...", command=callback)

    mainloop()
    time.sleep(3)
#

main()

Upvotes: 1

Views: 5275

Answers (1)

tobias_k
tobias_k

Reputation: 82889

There are two problems with your code:

  • Your callback method never finishes (due to the infinite loop), causing the GUI to freeze. Instead, use the after method to schedule another execution of callback after the method finishes.
  • Your stopit method creates a local variable s instead of changing the global one. Use the global keyword to fix this.

Change the two methods to something like this, and it should work:

def stopit():
    global s
    s = 1
    print "stopped"

def callback():
    if s == 0:
        print "called the callback!"
        root.after(3000, callback)

Upvotes: 2

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