CODEWITHSUNDEEP
pythontkinterprintingprogress-barprogress
AleBares
AleBares

Reputation: 1

Why does my progress bar work with "print" command and not with tkinter?

I would like to understand why this code: 

import time

for i in range(1,11):
    print(i)
    time.sleep(1)

shows (as it should!) numbers from 1 to 10, each every 1 second, while this code:

from tkinter import *
import time

root = Tk()

for i in range(1,11):
    Label(root, text = i).grid(row=0, column=i-1, padx=5, pady =5)
    time.sleep(1)

root.mainloop()

waits for 10 seconds, and then displays a window with the 10 numbers (instead of adding them one by one). I am aware this is a silly question, but I really can't understand! Many Thanks! Alessandro

Upvotes: 0

Views: 246

Answers (2)

CrazySqueak
CrazySqueak

Reputation: 611

This is because the time.sleep function is before the root.mainloop function.

root.mainloop is what causes the window to appear on-screen and start doing things. Instead, I'd recommend using window.after, as that tells the window to run a function after some time when it's on-screen.

Here's an example of a modification you could make (it's not that good but it works):

from tkinter import *
import time

root = Tk()
progress = 0
end = 10

def update_progress():
    global progress
    progress += 1
    Label(root, text = progress).grid(row=0, column=progress-1, padx=5, pady =5)
    if progress < end: root.after(1000,update_progress)  # Tell the window to call this function in 1000ms (1 second)

root.after(0,update_progress)  # Tell the window to run the update_progress function 0ms after now.
root.mainloop()

I'd recommend looking at gelonida's answer for an explanation of why your original code didn't work, and what you need to keep in mind when programming with GUIs in the future.

Upvotes: 3

gelonida
gelonida

Reputation: 5630

Most GUI's work differently to what you expect.

They work in an asynchronous way, which means, that you setup your windows and start an event loop. This event loop will display all widgets, labels, etc, that you set up before calling the event loop and wait for any events (GUI events like mouse or keyboard events, timer events and perhaps network events).

When any event is encountered code associated to that event will be called and this code can request to change the GUI (show or hide elements, change labels or attributes of graphical widgets) However the change to the GUI will only be performed when you give control back to the event loop (when the code handling an event finished)

In your given code you change a label in a for loop with sleep statements, but only after the for loop is finished your main loop is being called and this is the moment, where the final state of your GUI will be displayed.

So what you encounter is a know issue for almost all GUI / asynhronous kind of applications.

You have to rewrite your code such, that you start a timer event, and when the timer event fires a function will set a label and increase the counter by 1. And if the counter is not 11 it will restart another timer

Upvotes: 3

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