Issue 36178: type.init called instead of cls.init when inheriting from type. (original) (raw)

I may be completely misunderstanding here, but: here's a reproducible example:

class MyMeta(type): def new(cls, *args, **kwargs): print('new', *args, **kwargs) super().new(cls, *args, **kwargs)

def __init__(self, a):
    print('__init__', *args, **kwargs)
    super().__init__(*args, **kwargs)

class A(metaclass=MyMeta): pass

MyMeta('A', (), {'module': 'main', 'qualname': 'A'})

Output:

new A () {'module': 'main', 'qualname': 'A'} new A () {'module': 'main', 'qualname': 'A'}

Is this by design?

Your metaclass.new method returns None instead of the new class. The rule for calling init is:

if the constructor new returns an instance of the type, then call the initializer init
otherwise, don't call init at all.

Since your new accidentally returns None, the init is not called. If you change the line to say

return super().new(cls, *args, **kwargs)

you will see that init is called. (And discover the bugs in your init method :-)