[Python-Dev] Deprecated __cmp__ and total ordering
Michael Foord
fuzzyman at voidspace.org.uk
Tue Mar 10 15:40:36 CET 2009
Raymond Hettinger wrote:
>
> [Mart Sõmermaa]
>>>> To provide total ordering without __cmp__ one has to implement all of
>>>> __lt__, __gt__, __le__, __ge__, __eq__ and __ne__. However, in all
>>>> but a few cases it suffices only to provide a "real" implementation
>>>> for
>>>> e.g. __lt__ and define all the other methods in terms of it as
>>>> follows:
>
> [Raymond Hettinger]
>>> FWIW, I'm working on a solution for the problem using class decorators.
>>> The idea is that it would scan a class and fill-in missing methods
>>> based
>>> on the ones already there. That way, any one of the four ordering
>>> relations can be provided as a starting point and we won't have to
>>> annoint one like __lt__ as the one true underlying method.
>>>
>>> When it's ready, I'll bring it to python-dev for discussion.
>
> [Michael Foord]
>> Is there something you don't like about this one:
>> http://code.activestate.com/recipes/576529/
>
> Yes, that recipe has the basic idea!
>
It was originally written after you issued a challenge at PyCon UK last
year.
> I think the implementation can be cleaned-up quite a bit
> and it can be made as fast as hand-written code (not
> the setup time, but the actual introduced method).
OK
I'll take it back to Christian and Menno and see what we can come up with.
Michael
>
>
> Raymond
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