QObject is not usable in __init__() of classes after the QObject in MRO

Consider the following code (see attachment for full working code):

class A:
    def __init__(self):
        super().__init__()

class B(QObject, A):
    def __init__(self, parent=None):
        super().__init__(parent)

Any class after the QObject in the MRO can not make use of the QObject inside their __init__(): None of the QObject’s methods work, self can not be used as parent for another QObject and str(self)/repr(self) fail.

Looking at the bindings code generated by Shiboken, this is because Shiboken::callInheritedInit() – which implements super() – is called before before the underlying C++ QObject is created. SIP does the opposite. That is, in PyQt one can use the QObject in __init__() of classes which follow the QObject in the MRO.