Multimethods in Python < http://www.artima.com/weblogs/viewpost.jsp?thread=101605 >

mm.py

registry = {}

class MultiMethod(object):
	def __init__(self, name):
		self.name = name
		self.typemap = {}
	def __call__(self, *args):
		types = tuple(arg.__class__ for arg in args) # a generator expression!
		function = self.typemap.get(types)
		if function is None:
			raise TypeError("no match")
		return function(*args)
	def register(self, types, function):
		if types in self.typemap:
			raise TypeError("duplicate registration")
		self.typemap[types] = function

def multimethod(*types):
	def register(function):
		name = function.__name__
		mm = registry.get(name)
		if mm is None:
			mm = registry[name] = MultiMethod(name)
		mm.register(types, function)
		return mm
	return register

mm_test.py

from mm import multimethod

@multimethod(int, int)
def foo(a, b):
	print '2 integral numbers: %s' % str((a, b))

@multimethod(float, float)
def foo(a, b):
	print '2 float numbers: %s' % str((a, b))

@multimethod(str, str)
def foo(a, b):
	print '2 strings: %s' % str((a, b))

if __name__ == '__main__':
	foo(1, 2)
	foo(1.0, 2.0)
	foo('a', 'b')

	foo(1, 2.0) # TypeError: no match