Why does this simple Tkinter code create two top-level windows?

Question

Consider this very simple code snippet:

import tkinter as tk

class GUI:
    def __init__(self):
        self.top_level_window = tk.Tk()
        

GUI()
GUI().top_level_window.mainloop()

It creates two top-level windows on my screen. Why?

I thought the first instance would be immediately garbage collected, so that I would only get one window. I have also tried slightly modified version, which I was sure for would create two separate objects, and thus only one window:

a=GUI()
b=GUI()
b.top_level_window.mainloop()

but I was wrong. And I can't think of a reason.

Any help?

[This may help](https://stackoverflow.com/questions/75195049/creating-diferent-wimdows-as-parameters-with-its-owm-variables) — Collaxd, Jan 22 '23 at 15:25

score 3 · Answer 1 · answered Jan 22 '23 at 17:03

You are saying

   GUI()
   GUI().top_level_window.mainloop()

Which is two windows because you called the class twice like Frost Dream said so all you need to do is delete GUI()

import tkinter as tk

class GUI:
    def __init__(self):
        self.top_level_window = tk.Tk()
        

GUI().top_level_window.mainloop()

score 1 · Answer 2 · answered Jan 22 '23 at 14:58

I think that with tkinter, the framework itself keeps hold of instances of GUI objects that you create. This defeats any garbage collection that you might assume is going to happen.

You would need to call .destroy() on any elements you want tkinter to forget.

score 1 · Answer 3 · answered Jan 22 '23 at 18:35

I thought the first instance would be immediately garbage collected

The python object that is the instance of GUI is garbage-collected. However, tkinter creates objects inside of an embedded tcl interpreter, and the tcl interpreter doesn't know anything about python objects. So, while the object is removed from python, the widgets still exist inside the tcl interpreter.

Put another way, garbage collect of a python object doesn't guarantee that the underlying tcl object is deleted. If you want the first window to be destroyed, you must call destroy() on the instance.

score 0 · Answer 4 · answered Jan 22 '23 at 14:54

0

Because you called the class two times.

GUI()
GUI().top_level_window.mainloop()
>>>
GUI().top_level_window.mainloop()

answered Jan 22 '23 at 14:54

This doesn't address OP's idea about garbage collection, nor does it explain the behaviour of the second code snippet. – Karl Knechtel Jan 22 '23 at 15:03

Why does this simple Tkinter code create two top-level windows?

4 Answers4