class classproperty:
    @contract
    def __init__(self, fget: Callable, doc=None):
        self._fget = fget
        if doc is None:
            doc = fget.__doc__
        self.__doc__ = doc

    def __get__(self, instance, cls):
        if cls is None:
            cls = type(instance)
        return self._fget(cls)

    def __set__(self, instance, value):
        raise AttributeError()

    def __delete__(self, instance):
        raise AttributeError()

class ClasspropertyTest(TestCase):
    class Foo:
        _bar = 'Bar'

        @classproperty
        def bar(cls):
            return cls._bar

    def test(self):
        self.assertEquals(self.Foo.bar, 'Bar')

    def testSet(self):
        with self.assertRaises(AttributeError):
            self.Foo.bar = 'Not bar'

    def testDelete(self):
        with self.assertRaises(AttributeError):
            del self.Foo.bar