Makes sense. I don't think we can ever be completely correct here since we're inferring intent from the presence of __init__/__new__ that's liable to be wrong in some cases, but it's likely correct often enough that it's worth doing.

If I understand correctly, we want to be more forgiving iff one of the two methods is used, so it seems like we should be complaining if both are used *or* if neither is used. After all, I could add a __new__ to my coop use case and I'd still want object to complain. If that's the case, both object_new and object_init should be complaining if ((tp->tp_new == object_new && tp->tp_init == object_init) || (tp->tp_new != object_new && tp->tp_init != object_init)).

Of course, for the paranoid, there's always the risk that __new__ will modify these class functions and change the outcome :) For instance, if a class had a __new__ and no __init__ and its __new__ changed __new__ back to object.__new__, object_init on that run would be fooled into thinking it's using the defaults for both and would complain. I think this could only be fixed in type_call, which is rather ugly...but then, this *is* a special case of the "call __init__ after __new__" behavior, and we're trying to solve it within the methods themselves. Perhaps this last point is academic enough to be ignored...I don't know why anyone would do this, although the language makes it possible.