[Python-Dev] Re: Re: lists v. tuples

[Raymond Hettinger]

> [Andrew Koenig]
> > Yes.  If you want to present a 3-way comparison to users, an
> > underlying 3-way comparison is the fastest way to do it.  The trouble
> > is that a 3-way comparison is definitely not the fastest way to
> > present a 2-way comparison to users.
> > 
> > So if you want users to see separate 2-way and 3-way comparisons,
> > I think the fastest way to implement them is not to try to force
> > commonality where none exists.
> 
> This seems an argument for keeping both __cmp__ and the six __lt__
> etc.  Yet TOOWTDI makes me want to get rid of __cmp__.

Recent experience with sets.py shows that __cmp__ has a high
PITA factor when combined rich comparisons.  There was no
good way to produce all of the desired behaviors:

 *  <, <=, >, >=  having subset interpretations
 *  __cmp__ being marked as not implemented
 * cmp(a,b) not by-passing __cmp__ when __lt__ and __eq__
    were defined.

The source of the complications is that comparing Set('a') and Set('b')
returns False for *all* of  <, <=, ==, >=, >.  Internally, three-way
compares relied on the falsehood of some implying the truth of
others.


Raymond Hettinger


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