The situation appears to be at least slightly different from what Guidostated. In 3.x, all classes subclass object, which has .__ne__, so ifthat stopped inferred != behavior, it would never happen.>>> class A:def __eq__(s,p): return 1>>> id(object.__ne__)10703216>>> id(A.__ne__)10703216No new A.__ne__ added.  But>>> c,d=object(),object()>>> c==dFalse>>> c!=dTrue>>> a,b = A(),A()>>> a==b1>>> a!=bFalseSo it seems that a!=b *is* evaluated as not a==b rather than asa.__ne__(b). If so, my revised suggested replacement would be:"There is one implied relationship among comparison operators: defining__eq__ causes '!=' to be evaluated as 'not ==' (but not the other way). There is no similar relationship for the order comparisons."I am a bit puzzled though. Inttp://svn.python.org/view/python/branches/py3k/Python/ceval.c?revision=73066&view=markupI traced compare_op to cmp_outcome to (in object.c) PyOjbect_RichCompareto do_richcompare to class specific tp_richcompare and I do not see thespecial casing of eq. However, I am newbie at codebase.