How can I replace a variable using a "for" loop and a time delay? I'm using Python and Tkinter

There are two ways I would do this. One is using a list of words and after() and the other would be adding dots to the end of the sentence.

Method 1:To begin with, create a list that has all the transitional words:

transition = ['Loading','Loading.','Loading..','Loading...','Loading....','Loading.....']

and now you need to index this list and call each item on the label, like:

count = 0 #a number to index the listdef new_window():    new_windy = Toplevel(main_window)    new_windy.title("New_Windy")    new_windy.geometry("200x200")    def change():        global count #globalize it        rep = main_window.after(1000,change) #repeat the function every 1 second        try: #to catch the index error            label.config(text=transition[count]) #change the text with the list index        except IndexError: #to get past the error showing up            main_window.after_cancel(rep) #stop the repetition if no more items left to show        count += 1 #increase the number by 1 over each repetition            label = Label(new_windy, text=transition[count]) #initially set the text to first element    label.pack()    change() #call the function for the first timetransition = ['Loading','Loading.','Loading..','Loading...','Loading....','Loading.....']

Method 2:There is also another method like you did using += '.'. That would be like:

def new_window():    global text #globalize the main text        new_windy = Toplevel(main_window)    new_windy.title("New_Windy")    new_windy.geometry("200x200")    text = 'Loading' #set the main text     def change():        global text #globalize the new text        text += '.' #add . over each iteration        rep = main_window.after(1000,change) #repeat the function every 1 second        label.config(text=text) #change the text to new text        if len(text) >= 7+5: #here 7 is the length of word 'Loading' and 5 is the maximum number of dots needed.            main_window.after_cancel(rep) #stop repeating the function    label = Label(new_windy, text=text) #set the main text at first    label.pack()    change() #call the function initially.

Now to some explanation:

but it is not quite behaving as it should.

That is because time.sleep() messes with mainloop() causing the unresponsiveness. Hence the GUI freezes, so instead we have to use a after() that does not freeze the GUI. Not only time.sleep(), also while and for loops mess with mainloop() causing the GUI to be unresponsive.

it just creates 10 versions of the word "loading" stacked on itself with successive numbers of full stops.

That is because every time the code is run, a new label is created with the text "Loading", what you want to do is, create the text once, and use config() to change the text later.

As a matter of fact your imports will cause you trouble later on, you are over writing tkinter widgets with widgets from ttk, so change you import statement and adjust the code accordingly, like:

import tkinter as tkfrom tkinter import ttk

Now if you want a tkinter widget use, tk.Label() or if you want a ttk widget, use ttk.Label() and so on.

use label.config() in order to edit a label which is already packed.

from tkinter import *from tkinter.ttk import *from tkinter import Button, Tk, HORIZONTALimport timedef new_window():    variable_text = "Loading"    new_windy = Toplevel(main_window)    new_windy.title("New_Windy")    new_windy.geometry("200x200")    label = Label(new_windy, text=variable_text)    for i in range(10):        time.sleep(0.3)        new_windy.update_idletasks()        variable_text += "."        label.config(text=variable_text)        label.pack()main_window = Tk()main_window.title("AWESOME_SAUCE")main_window.geometry('600x600')button = Button(main_window, text="click_me", command=new_window)button.pack()main_window.mainloop()

As per your requirement of "Loading" showing first when the window pops up and then later after sometime the "." appearing, for this we can consider it as two processes. In the first one we need to print "Loading" and then the ".". For this I have kept the for loop to iterate twice and for the 2nd time, time.sleep() is used to provide some time in there before "." appears.

Refer the following modified code please

from tkinter import *from tkinter.ttk import *from tkinter import Button, Tk, HORIZONTALimport timedef new_window():    variable_text = "Loading"    new_windy = Toplevel(main_window)    new_windy.title("New_Windy")    new_windy.geometry("200x200")    label = Label(new_windy, text=variable_text)    for i in range(2):        new_windy.update_idletasks()        if i == 1:            time.sleep(3)            variable_text += "."        label.config(text=variable_text)        label.pack()main_window = Tk()main_window.title("AWESOME_SAUCE")main_window.geometry('600x600')button = Button(main_window, text="click_me", command=new_window)button.pack()main_window.mainloop()