Alternative To Time.Sleep() for pausing a function

Question

I created an example code because my original is too big and has private information(My own) in it.

While running a program from a Tkinter GUI, it runs the program but makes the GUI unresponsive because of time.sleep() blocking the GUI from updating.

I am trying to avoid using timers because it fires a different function after a duration instead of simply pausing the function and then continuing the same function.

Is there an alternative that does not block the GUI but still adds a delay inside of the function?

Example Code:

from tkinter import *
import time

wn = Tk()
wn.geometry("400x300")
MyLabel = Label(wn, text="This is a Status Bar")
MyLabel.pack()

def MyFunction():
    Value = 1
    while Value < 10:
        print("Do something")
        time.sleep(1) **# - here blocks everything outside of the function**
        MyLabel.config(text=Value)
        # A lot more code is under here so I cannot use a timer that fires a new function
    Value = 1

MyButton = Button(wn, text="Run Program", command=MyFunction)
MyButton.pack()

wn.mainloop()

Edit: Thanks so much, you're answers were fast and helpful, I changed the code and added "wn.mainloop()" after the delay and replaced "time.sleep(1)" with wn.after(100, wn.after(10, MyLabel.config(text=Value))

here is the final code:

from tkinter import *
import time

wn = Tk()
wn.geometry("400x300")
MyLabel = Label(wn, text="This is a Status Bar")
MyLabel.pack()

def MyFunction():
    Value = 0
    while Value < 10:
        print("Do something")
        wn.after(10, MyLabel.config(text=Value))
        Value += 1
    wn.mainloop()

MyButton = Button(wn, text="Run Program", command=MyFunction)
MyButton.pack()

wn.mainloop()

There is no way to do this within a function - if you don't return to Tkinter's mainloop, then the GUI is frozen. The proper solution is to use `.after()` (the version with 2+ parameters) to schedule a function for later execution - yes, this does require a rather different structure to your program. — jasonharper, Feb 14 '22 at 19:28
Another approach would be to use a thread and event queue model, where your `MyFunction` runs in a separate thread. There's also the option of using async/await in a separate thread (and `asyncio.sleep`); see https://stackoverflow.com/questions/49958180/using-async-await-keywords-with-tk-after-method-of-tkinter for a recipe. — nneonneo, Feb 14 '22 at 19:32
`wn.after(10, MyLabel.config(text=Value)` doesn't do what you think it does. `wm.after(10, MyLabel.config(text=Value)` runs the configure step immediately. — Bryan Oakley, Feb 14 '22 at 20:17

score 1 · Answer 1 · answered Feb 14 '22 at 19:28

The short answer is that you can use wn.after() to request a callback after a certain amount of time. That's how you handle it. You get a timer tick at a one-per-second rate, and you have enough state information to let you proceed to the next state, then you go back to the main loop.

Put another way, timers are exactly how you have to solve this problem.

score 1 · Answer 2 · answered Feb 14 '22 at 19:37

Fundamentally, any callback function in Tkinter runs in the main GUI thread, and so the GUI thread will block until the function exits. Thus you cannot add a delay inside the function without causing the GUI thread to be delayed.

There are two ways to solve this. One would be to refactor your function into multiple pieces so that it can schedule the remaining work (in a separate function) via .after. This has the advantage of ensuring that all of your functions are running in the main thread, so you can perform GUI operations directly.

The other way is to run your function in a separate thread that is kicked off whenever your main callback is executed. This lets you keep all the logic inside the one function, but it can no longer perform GUI operations directly - instead, any GUI operations would have to go through an event queue that you manage from the main thread.

acw1668 · Answer 3 · 2022-02-15T09:47:14.053

You can combine after() and wait_variable() to simulate time.sleep() without blocking tkinter from handling pending events and updates:

def tk_sleep(delay):
    v = wn.IntVar()
    # update variable "delay" ms later
    wn.after(delay, v.set, 0)
    # wait for update of variable
    wn.wait_variable(v)

Using tk_sleep() in your while loop:

def MyFunction():
    Value = 1
    while Value < 10:
        print("Do something")
        tk_sleep(1000) # waits for one second
        MyLabel.config(text=Value)
        # A lot more code is under here so I cannot use a timer that fires a new function
        Value += 1

Alternative To Time.Sleep() for pausing a function

3 Answers3