There's more...

We subclassed the Tk class in our example, but it is also common to subclass other widget classes. We did this to reproduce the same statements that we had before we refactored the code.

However, it may be more convenient to subclass Frame or Toplevel in larger programs, such as those with multiple windows. This is because a Tkinter application should have only one Tk instance, and the system creates one automatically if you instantiate a widget before you create the Tk instance.

Keep in mind that this decision does not affect the structure of our App class since all widget classes have a mainloop method that internally starts the Tk main loop.