About Me

PBX My name is Paul Bissex, and e-scribe.com is my consulting business. I build web applications using as much open source software as possible. From September to June I teach web design and other important non-photographic professional skills to photographers. In the '90s I wrote technology commentary and reviews for magazines, newspapers, and web publications, including Wired, Salon.com, FamilyPC, the late lamented Web Review, and the Chicago Tribune. Feel free to email me.

Book

I'm co-author of "Python Web Development with Django", an excellent guide to my favorite web framework. Its strong points include an introduction to Python, and better coverage of Django 1.0 than nearly anybody else. Published by Addison-Wesley, it is available from Amazon and your favorite technical bookstore as well.

Colophon

This runs on Django, served by Apache and mod_python. The database is SQLite. The operating system is FreeBSD, on a VPS hosted at Johncompanies.com. Comment-spam protection by Akismet. Vintage topo imagery from the Maptech archive. The markup engine is Markdown.

Pile o'Tags

Stuff I Use

Akismet, del.icio.us, Django, dpaste.com, Emacs, FreeBSD, Freenode, jQuery, LaunchBar, MacPorts, Markdown, Mercurial, OS X, Postfix, Python, SQLite, Subversion, TextMate, Trac, Ubuntu Linux, wmii

Spam Report

At least 59046 pieces of comment spam killed since January 2008, mostly via Akismet.

99 problems

There is a classic set of programming exercises called "Ninety-Nine Prolog Problems". Though somewhat tailored to logic programming, they form an interesting set of exercises for other languages. I've seen adaptations of varying completeness for Haskell, Lisp, Perl 6, and Python.

I was reminded of this all by a recent blog post by some bloke called Dave who was using the problems as a way to become more familiar with Python. He used Python's unittest module to test his solutions.

I actually played with these same problems in Python a while ago (before I had found that collection on the Python wiki), and like Dave I decided to incorporate tests. Instead of unittest, though, I used doctest, so the test cases live in the docstring with the description of the problem. For example:

def p31(n):
    """
    P31 (**) Determine whether a given integer number is prime.

    >>> p31(7) and p31(2) and p31(31)
    True
    >>> p31(1) or p31(4) or p31(9)
    False
    """
    if n < 2:
        return False
    for i in range(2, n/2 + 1):
        if n % i == 0:
            return False
    return True

(No, not the most efficient algorithm!)

I collected all the problems in a single module. At the end is the code that invokes the doctest runner:

if __name__ == '__main__':
    import doctest
    doctest.testmod()

One motivation for this structure was the idea that I could build a version of the module with just the docstrings and pass function bodies as a blank slate for people who wanted to try their hand at the problems.

I got through about 40 problems, but it's unlikely I'll have the time to finish them any time soon (life got busy, and they get harder as you go). The source is here for anyone who feels like continuing the project, or using the doctest idea to enhance the version on the Python wiki. Keep me posted if you do!

Wednesday, April 2nd, 2008
education + programming + prolog + python
3 comments