Python tkinter after method not working as expected

Question

I'm trying to learn Tkinter module, but I can't undestand why the after method doesn't behave as expected. From what I know, it should wait ms milliseconds and then execute the function, but in my case the function gets executed many more time, not considering the time I write. Here's the code:

from tkinter import *

def doSomething():
    x = int(l["text"])
    l["text"] = str(x + 1)

root = Tk()
root.geometry("300x300")
l = Label(root, text="0")
l.pack()

while True:
    l.after(1000, doSomething)
    root.update()
    if int(l["text"]) >= 5:
        break

root.mainloop()

After the first 2 seconds the label starts displaying humongous numbers

What is the purpose of while True, instead, you can move your if and root.after() inside the func. — Delrius Euphoria
– Delrius Euphoria, Commented Apr 3, 2021 at 10:15

Delrius Euphoria · Accepted Answer · 2021-04-03 10:28:24Z

2

After the first 2 seconds the label starts displaying humongous numbers

Keep in mind, while True, is an infinite loop, you are making infinite calls to root.after() means alot of events are being scheduled to be called after 1 second. Better way to do this is to remove your while and move it all inside your function.

from tkinter import *

root = Tk()

def doSomething():
    x = int(l["text"])
    l["text"] = x + 1
    if int(l["text"]) < 5: # Only repeat this function as long as this condition is met
        l.after(1000, doSomething)

root.geometry("300x300")
l = Label(root, text="0")
l.pack()

doSomething()

root.mainloop()

Though the best way to write the function would be to create a variable and increase the value of that variable inside the function and then show it out:

from tkinter import *

root = Tk()

count = 0 # Initial value
def doSomething():
    global count # Also can avoid global by using parameters
    count += 1 # Increase it by 1 
    l['text'] = count # Change text
    if count < 5:
        l.after(1000, doSomething)

root.geometry("300x300")
l = Label(root, text=count)
l.pack()

doSomething() # If you want a delay to call the function initially, then root.after(1000,doSomething)

root.mainloop()

This way you can reduce the complexity of your code too and make use of the variable effectively and avoid nasty type castings ;)

edited Apr 3, 2021 at 10:28

answered Apr 3, 2021 at 10:22

Delrius Euphoria

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4 Comments

Fra Sassone Over a year ago

Thanks a lot! So I guess the best way to call after is inside a function, so that it can be executed as long as a certain condition is met, right? Because I don't understand why using the while True loop is a bad idea in this case. I get that i'm making infinite calls, but why isn't the method executing one call per second, as stated in the after(1000, doSomething)?

Delrius Euphoria Over a year ago

@FraSassone while does not wait 1 second for doSomething to get executed. As long as while is concerned, root.after() is just a line of code that does not stop it. One way to pause while in between is to use time.sleep() but it also has its disadvantages, always better to use after() and avoid while at all costs.

Delrius Euphoria Over a year ago

@FraSassone ~ Would appreciate marking this as the correct answer if this answered your questions correctly. Click here to learn how :D

Fra Sassone Over a year ago

Oh I'm sorry! I'm new here, thanks for the clarification <3

Anuj Sharma · Accepted Answer · 2021-04-03 10:26:07Z

1

You are using infinite loop when using while True. Correct way is:

from tkinter import *

def doSomething():
    x = int(l["text"])
    l["text"] = str(x + 1)
    if x < 5:
        l.after(1000, doSomething)

root = Tk()
root.geometry("300x300")
l = Label(root, text="0")
l.pack()


doSomething()


root.mainloop()

answered Apr 3, 2021 at 10:26

Anuj Sharma

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