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Programming Python, 3rd Edition
book

Programming Python, 3rd Edition

by Mark Lutz
August 2006
Intermediate to advanced content levelIntermediate to advanced
1600 pages
51h 46m
English
O'Reilly Media, Inc.
Content preview from Programming Python, 3rd Edition

Step 4: Adding Console Interaction

So far, our database program consists of class instances stored in a shelve file, as coded in the preceding section. It’s sufficient as a storage medium, but it requires us to run scripts from the command line or type code interactively in order to view or process its content. Improving on this is straightforward: simply code more general programs that interact with users, either from a console window or from a full-blown graphical interface.

A Console Shelve Interface

Let’s start with something simple. The most basic kind of interface we can code would allow users to type keys and values in a console window in order to process the database (instead of writing Python program code). Example 2-21, for instance, implements a simple interactive loop that allows a user to query multiple record objects in the shelve by key.

Example 2-21. PP3E\Preview\peopleinteract_query.py

# interactive queries
import shelve
fieldnames = ('name', 'age', 'job', 'pay')
maxfield   = max(len(f) for f in fieldnames)
db = shelve.open('class-shelve')

while True:
    key = raw_input('\nKey? => ')       # key or empty line, exc at eof
    if not key: break
    try:
        record = db[key]                # fetch by key, show in console
    except:
        print 'No such key "%s"!' % key
    else:
        for field in fieldnames:
            print field.ljust(maxfield), '=>', getattr(record, field)

This script uses getattr to fetch an object’s attribute when given its name string, and the ljust left-justify method of strings to align outputs (maxfield, derived ...

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Publisher Resources

ISBN: 0596009259Supplemental ContentErrata Page