Hi list, while a class is being initialized in a metaclass, it is not always possible to call classmethods of the class, as they might use super(), which in turn uses __class__, which is not initialized yet.
I know that this is a known issue, but well, sometimes it even makes sense to fix already known issues... so I wrote a patch that moves the initialization of __class__ into type.__new__, so that one may use super() in a class once it starts existing. It's issue 23722 on the issue tracker. To illustrate what the problem is, the following code raises a RuntimeError: class Meta(type): def __init__(self, name, bases, dict): super().__init__(name, bases, dict) self.f() class A(metaclass=Meta): @classmethod def f(self): super() it works fine with my patch applied. Technically, my patch slightly changes the semantics of python if a metaclass returns something different in its __new__ than what type.__new__ returns. But I could not find any documentation of the current behavior, and also the tests don't test for it, and I consider the current behavior actually buggy. As an example let me give the following simple Singleton metaclass: class Singleton(type): def __new__(cls, name, bases, dict): return super().__new__(cls, name, bases, dict)() class A(metaclass=Singleton): def test(self): assert(isinstance(__class__, type)) A.test() The current python fails the assertion, while with my patch everything is fine, and I personally think __class__ should always actually refer to the class being defined, which means at the minimum that it is actually, well, a class. Greetings Martin _______________________________________________ Python-Dev mailing list [email protected] https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com