Is it necessary to call Tk() when writing a GUI app with Tkinter?

[John Salerno]

> EXAMPLE 1: (this works, but is flawed!)
>  root = tk.Tk()
>  b = tk.Button(master=None, text='Sloppy Coder')
>  b.pack()
>  root.mainloop()
> 
> EXAMPLE 2: (This is how to write code!)
>  root = tk.Tk()
>  widgetframe = tk.Frame(root)
>  b = tk.Button(master=None, text='Sloppy Coder')
>  b.pack()
>  root.mainloop()
> 
> EXAMPLE 3: (OOP style)
>  class App(tk.Tk):
>      def __init__(self):
>          tk.Tk.__init__(self)
>          # something should happen here to justify using OOP
>      # or here
> 
>  class AppFrame(tk.Frame):
>      def __init__(self, master, **kw):
>          tk.Frame.__init__(self, master, **kw)
>          self.createWidgets()
> 
>      def createWidgets(self):
>          b = tk.Button(master=None, text='Push Me')
>          b.pack()
> 
>  if __name__ == '__main__':
>      app = App()
>      frame = AppFrame(app)
>      frame.pack()
>      app.mainloop()

Why is the master argument for Button set to None? Shouldn't it be the Frame object? And shouldn't it also have self as the first argument?