Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

I want to set a label in Tkinter using my countdown timer function. Right now all it does is set the lable to "10" once 10 is reached and I don't really understand why. Also, even if I have the timer print to a terminal instead the "Time's up!" bit never prints.

import time
import tkinter as tk
class App():
    def __init__(self):
        self.root = tk.Tk()
        self.label = tk.Label(text="null")
        self.label.pack()
        self.countdown()
        self.root.mainloop()
    # Define a timer.
    def countdown(self):
        p = 10.00
        t = time.time()
        n = 0
        # Loop while the number of seconds is less than the integer defined in "p"
        while n - t < p: 
            n = time.time()
            if n == t + p:
                self.label.configure(text="Time's up!")
            else:
                self.label.configure(text=round(n - t))
app=App()
Tkinter already has an infinite loop running (the event loop), and a way to schedule things to run after a period of time has elapsed (using after). You can take advantage of this by writing a function that calls itself once a second to update the display. You can use a class variable to keep track of the remaining time. 
import Tkinter as tk
class ExampleApp(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)
        self.label = tk.Label(self, text="", width=10)
        self.label.pack()
        self.remaining = 0
        self.countdown(10)
    def countdown(self, remaining = None):
        if remaining is not None:
            self.remaining = remaining
        if self.remaining <= 0:
            self.label.configure(text="time's up!")
        else:
            self.label.configure(text="%d" % self.remaining)
            self.remaining = self.remaining - 1
            self.after(1000, self.countdown)
if __name__ == "__main__":
    app = ExampleApp()
    app.mainloop()
                That explains a lot, thank you. I was wondering why it only updates once the last item is reached even after I rewrote it a few different ways.
– Ryan Hasse
                May 15, 2012 at 11:49
                @RyanHasse: the display only updates when Tkinter can respond to events that tell it to update the display. These events only get processed by the event loop. If you have your own loop, it will starve the event loop, preventing redraw requests from happening.
– Bryan Oakley
                May 15, 2012 at 12:54
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.