c3.py

def merge(classes_list):
    merged = [None]
    while classes_list:
        for classes in classes_list:
            head = classes[0]
            tails = [c[1:] for c in classes_list]
            if not any(head in tail for tail in tails):
                if head != merged[-1]:
                    merged.append(head)
                for classes in classes_list:
                    if head in classes:
                        classes.remove(head)
                    if not classes:
                        classes_list.remove(classes)
                break
        else:
            raise RuntimeError('Conflict! {}'.format(classes_list))

    return merged[1:]

def c3(c):
    linearized = [c3(b) for b in c.__bases__ if b]
    if c.__bases__:
        linearized.append(list(c.__bases__))
    return [c] + merge(linearized)


O = object
class F(O): pass
class E(O): pass
class D(O): pass
class C(D,F): pass
class B(D,E): pass
class A(B,C): pass

print c3(A)
print c3(A) == A.mro()

O = object
class F(O): pass
class E(O): pass
class D(O): pass
class C(D,F): pass
class B(E,D): pass
class A(B,C): pass

print c3(A)
print c3(A) == A.mro()


class FakeC(object):
    def __init__(self, *bases):
        self.__bases__ = bases

O = object
class X(O): pass
class Y(O): pass
class A(X,Y): pass
class B(Y,X): pass

print c3(A)
print c3(A) == A.mro()
print c3(FakeC(A, B))