This example is take from: http://www.python.org/2.3/mro.html

"Serious order disagreement" # From Guido class O: pass class X(O): pass class Y(O): pass class A(X,Y): pass class B(Y,X): pass try: class Z(A,B): pass #creates Z(A,B) in Python 2.2 except TypeError: pass # Z(A,B) cannot be created in Python 2.3