multiMethod.py

#From: Five-minute Multimethods in Python
# by Guido van van Rossum
# http://www.artima.com/weblogs/viewpost.jsp?thread=101605

#Modified to support inheritance

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
  

#class A(object):
#  pass
#
#class B(A):
#  pass  
#
#@multimethod(int,int)
#def foo(a,b):
#  print 'int'
#  
#@multimethod(A,A)
#def foo(a,b):
#  print 'works'
#  
#  
#a = A()
#b = B()  
#foo(a,b)