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

Terry Reedy tjreedy@udel.edu
Sat, 15 Mar 2003 12:54:05 -0500

"Guido van Rossum" <guido@python.org> wrote in message
> But the order isn't meaningful.
> If I had to do it over again, I'd only implement == and != for
> of vastly differing types, and limit <, <=, >, >= to objects that
> meaningfully comparable.

For user-defined types/classes, I presume that this would still mean
deferring to the appropriate magic method (__cmp__ or __ge__?) to
define 'meaningful'.

> I'd like to to this in Python 3.0, but that probably means we'd have
> to start deprecating default comparisons except (in)equality in
> 2.4.

+1, I think.

Based on reading cl.py, the validity of nonsense comparisons is one of
the more surprising 'features' of Python for beginners -- who
reasonably expect a TypeError or ValueError.  Once they get past that,
they are then surprised by the unstability across versions.  Given
that universal sorting of hetero-lists is now broken, I think it would
be better to do away with it cleanly.  It is seldom needed and would
still be available with a user-defined sorting function (which
requires some thought as to what is really wanted).  A Python version
of the present algorithm could be included (in Tools/xx perhaps) for
anyone who actually needs it.

Terry J. Reedy