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234 CHAPTER 10 ■ BATTERIES INCLUDED
■Caution As you can see, the program specifies the file name C:\database.dat. If you, by any chance,
have a database by that name that the shelve module can use, it will—and that database will be modified.
So make sure that you use a file name for your database that isn’t in use already. After running this program,
the proper file appears.
The program shown in Listing 10-8 has several interesting features:
• I have wrapped everything in functions to make the program more structured. (A possible improvement
is to group those functions as the methods of a class.)
• I have put the main program in the main function, which is called only if __name__ == '__main__'.
That means you can import this as a module and then call the main function from another program.
• I open a database (shelf) in the main function, and then pass it as a parameter to the other functions
that need it. I could have used a global variable, too, because this program is so small, but it’s better to
avoid global variables in most cases, unless you have a reason to use them.
• After reading in some values, I make a modified version by calling strip and lower on them because
if a supplied key is to match one stored in the database, the two must be exactly alike. If you always use
strip and lower on what the user enters, you can allow him or her to be sloppy about using uppercase
or lowercase letters and additional whitespace. Also, note that I’ve used capitalize when printing the
field name.
• I have used try and finally to ensure that the database is closed properly. You never know when
something might go wrong (and you get an exception), and if the program terminates without closing
the database properly, you may end up with a corrupt database file that is essentially useless. By using
try and finally, you avoid that.
So, let’s take this database out for a spin. Here is the interaction between the program and me:
Enter command (? for help): ?
The available commands are:
store : Stores information about a person
lookup : Looks up a person from ID number
quit : Save changes and exit
? : Prints this message
Enter command (? for help): store
Enter unique ID number: 001
Enter name: Mr. Gumby
Enter age: 42
Enter phone number: 555-1234
Enter command (? for help): lookup
Enter ID number: 001
What would you like to know? (name, age, phone) phone
Phone: 555-1234
Enter command (? for help): quit