Attached is a new patch, which includes Nick's logic from msg140493, some of the code readability changes Jim suggested in msg151989 (but not the behavioural changes), and associated tests. On Nick's advice, I have also replaced the dunder equals calls with the standard comparators (==/!=), given not all classes will necessarily have both NE and EQ, and made the comparison the last action in each method, for consistency.

Test cases have been added to check a TypeError is raised, rather than True being returned, when GE/LE is called on two objects that are equal but have a comparator that returns NotImplemented.