About Me

PBX I'm Paul Bissex, and e-scribe.com is my consulting business. I build web applications using open source software, especially Django. In the '90s I did graphic design for newspapers and magazines. Then I wrote technology commentary and reviews for Wired, Salon.com, Chicago Tribune, and lots of little places you've never heard of. Feel free to email me.

Book

I'm co-author of "Python Web Development with Django", an excellent guide to my favorite web framework. Published by Addison-Wesley, it is available from Amazon and your favorite technical bookstore as well.

Colophon

Built using Django, served by Apache and mod_wsgi. 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 70644 pieces of comment spam killed since January 2008, mostly via Akismet.

Neat Python hack: infix operators

I came across this neat Python hack on reddit today, a technique for defining arbitrary infix operators. Not overriding + or >> et al., but creating keyword-style pseudo-operators that... well, the code is probably as clear as any description I could come up with:

class infix(object):
    """
    Clever hack (slightly modified) for defining infix operators. 
    Via http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/384122
    Intended for use as a decorator.

    >>> @infix
    ... def removing(str, chars):
    ...     for char in chars:
    ...         str = str.replace(char, '')
    ...     return str
    ...
    >>> print 'Hello, world!' |removing| 'eo'
    Hll, wrld!
    """
    def __init__(self, function):
        self.function = function
    def __ror__(self, other):
        return infix(lambda x: self.function(other, x))
    def __or__(self, other):
        return self.function(other)
    def __call__(self, value1, value2):
        return self.function(value1, value2)

Some people hate this kind of stuff. That's why we call it a hack, to indicate that we don't think it's a great building block for your missile control software. Some of Those People still get their underoos in a bunch regardless. But you have to admit it's damned clever.

This also reminds me of some of the lovely higher-order-function features in Haskell, where you can make a regular (prefix) function into infix by wrapping it in backticks -- 10 `mod` 3 -- and an infix function (operator) into prefix by wrapping it in parentheses -- (+) 2 2.

Sunday, February 25th, 2007
fun + haskell + programming + python
5 comments

Some related posts: The Language I Will Kind of Learn in 2008: Smalltalk • Understanding tuples vs. lists in Python • Array comprehensions in Javascript • The whitespace brigade • 99-byte Python quicksort • Let's play a game: BASIC vs. Ruby vs. Python vs. PHP • Figlet Captcha • BASIC Computer Games • A Ruby happening • CodeZoo

• Comment from Justin , later that day

I totally hate it. :)

• Comment from James , 4 days later

I totally love it. :)

• Comment from Paul , 1 week later

Now *that's* what I call fair and balanced.

• Comment from bruce , 14 months later

` `

class infix2(object):
def __init__(self, function):
self.function = function
def __ror__(self, other):
self.value=other
return self
def __or__(self, other):
return self.function(self.value,other)

With this version, you do not instanciate a lambda object for each `__ror__` call. On my PC, it's 45% performance gain !

• Comment from Paul , 14 months later

I love that you profiled it.