class A(object):
    def __init__(self):
        self.a = 1
    def x(self):
        print "A.x"
    def y(self):
        print "A.y"
    def z(self):
        print "A.z"

class B(A):
    def __init__(self):
        A.__init__(self)
        self.a = 2
        self.b = 3
    def y(self):
        print "B.y"
    def z(self):
        print "B.z"

class C(object):
    def __init__(self):
        self.a = 4
        self.c = 5
    def y(self):
        print "C.y"
    def z(self):
        print "C.z"

class D(C, B):
    def __init__(self):
        C.__init__(self)
        B.__init__(self)
        self.d = 6
    def z(self):
        print "D.z"

Which __init__ methods are invoked and in which order is determined by the coding of the individual __init__ methods.

When resolving a reference to an attribute of an object that's an instance of class D, Python first searches the object's instance variables then uses a simple left-to-right, depth first search through the class hierarchy. In this case that would mean searching the class C, followed the class B and its superclasses (ie, class A, and then any superclasses it may have, et cetera).

With the definitions above if we define

obj = D()

then what is printed by each of the following statements?

    print obj.a

    print obj.b

    print obj.c

    print obj.d

    obj.x()

    obj.y()

    obj.z()