try:
# For Python 2.x
import Tkinter as tk
except ImportError:
# For Python 3.x
import tkinter as tk
app_win = tk.Tk()
app_win.title('Hello World')
app_frame = tk.Frame(app_win)
app_win.mainloop()
I don't understand the app_ prefix. This has (almost) nothing to do with this post... it's used everywhere. Obviously it's your app, why would you need to remind yourself of that. Wouldn't it make more sense, and be easier to read, if the variables were simply "win" and "frame"?