Serhiy on the PR: "This is overgeneralization. Can tp_dict be not exact dict at all? I don't think this is possible. In many places concrete dict API is used with tp_dict. If you want to allow tp_dict be not exact dict, please open a separate issue for this." Using the following code, A.__dict__ type is dict even if the metaclass creates a different type, probably because type_new() calls PyDict_Copy(orig_dict): --- class mydict(dict): def __setitem__(self, name, value): if name == "__module__": value = "<mock module>" super().__setitem__(name, value) class MetaClass(type): @classmethod def __prepare__(mcl, name, bases): return mydict() class A(metaclass=MetaClass): pass print(A.__module__) ---