multimethod.py

from collections import defaultdict
import functools

class multimethod(object):
    """
    multimethod.register('function', dispatcher)

    @multimethod.register('function')
        def dispatcher(): pass

    @multimethod(dispatch_value)
    def function(*args, **kwargs): pass
    """
    _dispatchers = {}
    _functions = defaultdict(dict)

    def __init__(self, dispatch_value):
        self._dispatch_value = dispatch_value

    def __call__(self, function):
        self._functions[function.__name__][self._dispatch_value] = function
        dispatcher = self._dispatchers[function.__name__]
        def proxy(*args, **kwargs):
            return self._functions[function.__name__][dispatcher(*args, **kwargs)](*args, **kwargs)
        return proxy

    @classmethod
    def register(cls, name, dispatcher=None):
        if dispatcher is not None:
            cls._dispatchers[name] = dispatcher
        else:
            return functools.partial(cls.register, name)

#Example

@multimethod.register('add_event')
def dispatch(event):
    return event['type']

@multimethod('game')
def add_event(event):
    print 'GAME'

@multimethod('event')
def add_event(event):
    print 'EVENT'
    
add_event({'type': 'game'}) # prints GAME