Another try to understand python MRO. Depth first?

mro.py

class A1(object):

    def __init__(self):
        print('A1>')
        super(A1, self).__init__()


class B1(A1):

    def __init__(self):
        print('B1>')
        super(B1, self).__init__()


class A2(object):

    def __init__(self):
        print('A2>')
        super(A2, self).__init__()


class B2(A2):

    def __init__(self):
        print('B2>')
        super(B2, self).__init__()


class Final(B1, B2):

    def __init__(self):
        print('Final>')
        super(Final, self).__init__()


f = Final()
# print: Final > B1 > A1 > B2 > A2

# if the resolution order isn't depth first the MRO should print
# Final > B1 > B2 > A1 > A2
# ???