update a variable in parent window after closing its toplevel window

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i want to update my variable in parent window when i close its toplevel window.
i cretaed a function "new_window"...this function creates a new window(Demo2 class) ...demo2 is a sample of Demo2 class...the "demo2.destroyed" is a variable for understanding whether the toplevel window was closed or not....
i recieved this error " 'int' object is not iterable"
why????
please help

my code is:

def new_window(self):
        
        demo2 = Demo2(self.master, self.var_sent)
        
        def check_demo2():
            if demo2.destroyed:
                
                global fasele
                global counter
                counter += fasele
        
                self.tyLabel.config(text=str(counter))
                
            else:
                self.master.after(100, check_demo2)

        check_demo2()]

Moderator:
added opening python code tag :-)