Core Python Programming (2nd Edition)

Lines 1943
The entire menu-driven application is controlled from the showmenu() function. Here, the user is
prompted with the menu options. Once the user makes a valid choice, the proper function is called. We
have not covered exceptions and try-except statement in detail yet, but basically that section of the
code allows a user to type ^D (EOF, which generates an EOFError) or ^C (interrupt to quit, which
generates a KeyboardInterrupt error), both of which will be processed by our script in the same manner
as if the user had typed the 'q' to quit the application. This is one place where the exception-handling
feature of Python comes in extremely handy. The outer while loop lets the user continue to execute
commands until they quit the application while the inner one prompts the user until they enter a valid
command option.
Lines 4546
This part of the code starts up the program if invoked directly. If this script were imported as a module,
only the functions and variables would have been defined, but the menu would not show up. For more
information regarding line 45 and the __name__ variable, see Section 3.4.1.
Here is a sample execution of our script:
$ stack.py
p(U)sh
p(O)p
(V)iew
(Q)uit
Enter choice: u
You picked: [u]
Enter new string: Python
p(U)sh
p(O)p
(V)iew
(Q)uit
Enter choice: u
You picked: [u]
Enter new string: is
p(U)sh
p(O)p
(V)iew
(Q)uit
Enter choice: u
You picked: [u]
Enter new string: cool!
p(U)sh
p(O)p
(V)iew