Core Python Programming (2nd Edition)

39 try:
40 choice =
raw_input(prompt).strip()[0].lower()
41 except (EOFError, KeyboardInterrupt):
42 choice = 'q'
43 print '\nYou picked: [%s]' % choice
44 if choice not in 'neq':
45 print 'invalid option, try again'
46 else:
47 chosen = True
48
49 if choice == 'q': done = True
50 if choice == 'n': newuser()
51 if choice == 'e': olduser()
52
53 if __name__ == '__main__':
54 showmenu()
Line-by-Line Explanation
Lines 13
After the Unix-startup line, we initialize the program with an empty user database. Because we are not
storing the data anywhere, a new user database is created every time this program is executed.
Lines 515
The newuser() function is the code that serves new users. It checks to see if a name has already been
taken, and once a new name is verified, the user is prompted for his or her password (no encryption
exists in our simple program), and his or her password is stored in the dictionary with his or her user
name as the key.
Lines 1724
The olduser() function handles returning users. If a user returns with the correct login and password, a
welcome message is issued. Otherwise, the user is notified of an invalid login and returned to the menu.
We do not want an infinite loop here to prompt for the correct password because the user may have
inadvertently entered the incorrect menu option.
Lines 2651
The real controller of this script is the showmenu() function. The user is presented with a friendly menu.
The prompt string is given using triple quotes because it takes place over multiple lines and is easier to
manage on multiple lines than on a single line with embedded '\n' symbols. Once the menu is
displayed, it waits for valid input from the user and chooses which mode of operation to follow based on
the menu choice. The try-except statements we describe here are the same as for the stack.py and
queue.py examples from the last chapter (see Section 6.14.1).
Lines 5354