class a(object):

    def __init__(self):

        print('in a')

class b(a):

    def __init__(self):

        print('in b')

        super().__init__()

        print('out b')

class c(a):

    def __init__(self):

        print('in c')

        super().__init__()

        print('out c')

class d(b, c):

    def __init__(self):

        print('in d')

        super().__init__()

        print('out d')

a = d()

print(a.__class__.mro())

[Running] python "d:\pyqt5\signal.py"

in d

in b

in c

in a

out c

out b

out d

(<class '__main__.d'>, <class '__main__.b'>, <class '__main__.c'>, <class '__main__.a'>, <class 'object'>)

def super(cls, inst):

    mro = inst.__class__.mro()

    return mro[mro.index(cls) + 1]