The simplegeneric module lets you define simple single-dispatch generic
functions, akin to Python's built-in generic functions like len(), iter() and so
on. However, instead of using specially-named methods, these generic functions
use simple lookup tables, akin to those used by e.g. pickle.dump() and other
generic functions found in the Python standard library.

WWW: https://pypi.python.org/pypi/simplegeneric