In order to conform to the object model, classes should define either no equality methods, or both an equality and an inequality method. If only one of __eq__ or __ne__ is defined then the method from the super class is used. This is unlikely to result in the expected behavior.

When you define an equality or an inequality method for a class, remember to implement both an __eq__ method and an __ne__ method.

In the following example the PointOriginal class defines an equality method but no inequality method. If this class is tested for inequality then a type error will be raised. The PointUpdated class is better as it defines both an equality and an inequality method. To comply fully with the object model this class should also define a hash method (identified by a separate rule).

Python Language Reference: object.__ne__, Comparisons.