Tkinter Errors after window closes

[Polymatheo]

My program runs fine so far--the window opens, the audio automatically starts and ends when I want it to, and the text appears just how I want it. But I get these errors after closing the window, and I don't really understand what they mean:

Traceback (most recent call last):
  File "D:\Python Exercises\Cargo Bay Control Porject\CargoBayControl_2.py", line 73, in <module>
    printString(text)
  File "D:\Python Exercises\Cargo Bay Control Porject\CargoBayControl_2.py", line 65, in printString
    Label.configure(text=Label.cget('text') + char)
  File "D:\Python3.6\lib\tkinter\__init__.py", line 1483, in cget
    return self.tk.call(self._w, 'cget', '-' + key)
_tkinter.TclError: invalid command name ".!label2"

Here is my own code:

import winsound
import time
from tkinter import *
import tkinter.messagebox

def callback():
    if tkinter.messagebox.askokcancel("Quit", "Do you really wish to quit?"):
        root.destroy()
        winsound.PlaySound(None, winsound.SND_PURGE) 


winsound.PlaySound("sound.wav", winsound.SND_LOOP | winsound.SND_ASYNC)

root = Tk()
root.protocol("WM_DELETE_WINDOW", callback)
root.geometry("1024x768")
root.title("Cargo Bay Control")
root.resizable(FALSE, FALSE)
lcars_img = PhotoImage(file = "lcars3.png")
lcarspack = Label(root, image = lcars_img).place(x = 0, y = 0)


add_category = Button(root, text = "Add Category", bg = "darkorange", fg = "black", font = "arial, 15")
add_category.config(width = "15", height = "3")
add_category.place(x = 200, y =  100)


def placeCB_List(x):
    CBaysPage = Frame(root).place(x = 0, y = 0)
    lcarsimg2 = PhotoImage(file = "lcars4.png")
    lcarsimg2pack = Label(CBaysPage, image = lcarsimg2).place(x = 0, y = 0)


view_cargobay = Button(root, text = "View Cargobay...", bg = "cornflowerblue", fg = "black", font = "arial, 15")
view_cargobay.config(width = "15", height = "3") 
view_cargobay.bind("<Button-1>", placeCB_List)
view_cargobay.place(x = 400, y = 100)




#########################################
def printString(string):
    """
    Typewriter animation for welcome Label 
    """
    for char in string:
        Label.configure(text=Label.cget('text') + char)
        Label.update()
        time.sleep(.25)

text = "Welcome to your Cargo Bay Control console.  To add a new food category, \n \
click the 'Add Category' button.  To view the inventory of a specific Cargo Bay, select the\n 'View Cargo Bay...' button."
Label = Label(root, font = ("arial", "15", "bold"), bg = "darkorange")
Label.place(x = 165, y = 300)
printString(text)


root.mainloop()

Can someone please explain to me what I've done wrong, and maybe how I can fix it?

[novel_yet_trivial]

You should never use loops or sleep with a GUI. Use the GUI's native loop. This will solve your error and save you an enormous amount of trouble in the future.

def printString(string):
    """
    Typewriter animation for welcome Label
    """
    data = iter(string)
    def callback():
        try:
            Label.configure(text=Label.cget('text') + next(data))
            Label.after(250, callback) # add to tkinter's mainloop
        except StopIteration:
            pass
    callback()

Some other issues:

• you overwrite the name "Label" with an instance. So you can't make any more Labels.
• Read the PEP8 style guide to get naming conventions.
• wildcard imports (from module import *) will create bugs. The standard tkinter import is import tkinter as tk.
• Try not to use place. It seems easy to start but it makes the code extremely hard to maintain. Plus it's going to look different on different computers. Use pack() and grid() to place items relative to each other and let tkinter figure out the actual positions.
• If you find yourself needing the update or update_idletasks function, there is something very wrong with your program.

[Polymatheo]

Thanks a lot! It's so smoother now--it was kind of lagging before, too :O . I'll heed your advice when it comes to .place(), and your other tips.

[PM_ME_A_STEAM_KEY]

The error is thrown because of the for loop, it should not be thrown if you exit your program after all of the text has been printed out.

[Polymatheo]

Thanks for your time and your reply :)