PEAK-Rules is a highly-extensible framework for creating and using
generic functions, from the very simple to the very complex. Out of
the box, it supports multiple-dispatch on positional arguments using
tuples of types, full predicate dispatch using strings containing
Python expressions, and CLOS-like method combining. (But the framework
allows you to mix and match dispatch engines and custom method
combinations, if you need or want to.)

WWW:	http://pypi.python.org/pypi/PEAK-Rules