gistfile1.py

import decorator

def multiplier(n):
    def decorator(fn):
        return Multiplier(fn, n)
    return decorator

class Multiplier(object):
    def __init__(self, func, n):
        self.func = func
        self.n = n
    def __call__(self, arg):
        return self.func(arg*self.n)
    def __get__(self, obj, type=None):
        if hasattr(self.func, '__get__):
            return self.__class__(self.func.__get__(obj, type), self.n)
        return self

@multiplier(3)
def foo(arg):
    print arg

foo(4)

class bar(object):
    @multiplier(4)
    def foo(self, arg):
        print self
        print arg
    
    @multiplier(5) # this won't work, since baz takes two arguments, but the decorator does not.
    def baz(self, arg):
        print self
        print arg

bar().foo(4)

bar().baz(5)