from functools import wraps
def interface (fn):
    @wraps
    def to_be_implemented (*args):
        raise Exception ("Interface '%s' is not implemented!" % fn.__name__)
    return to_be_implemented
class Foo (object):
    @interface
    def test (self): pass
class Bar(Foo):
    def test (self): pass
class Qux(Foo):
    pass
Bar().test()
Qux().test()