Continue executing function

When closing an instance of the ChildWindow class, which was called from another instance of MainWindow, the code does not continue to be executed.

I noticed that only when the MainWindow instance is closed does it continue to run. In general, it has a cumulative property, so the number of times the ChildWindow closes the window, the continuation will be displayed.

I want the function to continue executing when the ChildWindow closes, without closing the main window. Here's my code:

from tkinter import *

class MainWindow():

    def __init__(self):
        self.root = Tk()
        
    def run(self):
        Button(self.root, text='click', command=lambda:self.open_child_window()).pack()
        self.root.mainloop()

    def open_child_window(self):
        A = ChildWindow()
        A.run()
        print("why i'm not write?")

class ChildWindow():

    def __init__(self):
        self.root = Toplevel()

    def run(self):
        self.root.mainloop()


A = MainWindow()
A.run()

It seems to me that this is due to the self.root.mainloop() loop, so I was looking for how to stop it, the .quit(), .destroy() methods do not help.

Solution

It's called a nested event loop or modal loop. Use the mainloop() and quit() like this.

class ChildWindow():
    def __init__(self):
        self.root = Toplevel()

    def run(self):
        win = self.root
        def on_close():
            win.destroy()
            win.quit()
        win.protocol('WM_DELETE_WINDOW', on_close)
        win.mainloop()
        print('end of the nested loop')
...

You can also use wait_window() and destroy() like this.(The former runs a nested event loop until the window is destroyed.)

class ChildWindow():
    ...
    def run(self):
        win = self.root
        def on_close():
            win.destroy()
        win.protocol('WM_DELETE_WINDOW', on_close)
        win.wait_window()