How to do it...

To improve the modularity of our simple program, we will define a class that wraps our global variables:

import tkinter as tk 
 
class App(tk.Tk): 
    def __init__(self): 
        super().__init__() 
        self.btn = tk.Button(self, text="Click me!", 
                             command=self.say_hello) 
        self.btn.pack(padx=120, pady=30) 
 
    def say_hello(self): 
        print("Hello, Tkinter!") 
 
if __name__ == "__main__": 
    app = App() 
    app.title("My Tkinter app") 
    app.mainloop()

Now, each variable is enclosed in a specific scope, including the command function, which is moved as a separate method.