[Python-3000] Please re-add __cmp__ to python 3000

[Adam Olsen]

On 10/30/07, Steven Bethard <steven.bethard at gmail.com> wrote:
> On 10/30/07, Adam Olsen <rhamph at gmail.com> wrote:
> > cmp and __cmp__ are doomed, due to unorderable types now raising exceptions:
> >
> > >>> cmp(3, 'hello')
> > Traceback (most recent call last):
> >   File "<stdin>", line 1, in <module>
> > TypeError: unorderable types: int() < str()
> > >>> 3 == 'hello'
> > False
> >
> > A mixin for __cmp__ would be sufficient for scalars (where you can
> > avoid this exception and your size is constant), but not for
> > containers (which need to avoid inappropriate types and wish to avoid
> > multiple passes.)
>
> I don't understand this conclusion.  If you start comparing things
> that are unorderable, you'll get an exception.  But cmp() still makes
> sense when you compare other things::
>
>     >>> cmp((1, 'a', 4.5), (1, 'a', 6.2))
>     -1
>     >>> cmp([6, 5, 4], [6, 4, 5])
>     1
>
> I definitely don't want any cmp/__cmp__ implementation that swallows
> exceptions when the types don't align, e.g.::
>
>     >>> cmp((1, 'a'), ('a', 1))
>     Traceback (most recent call last):
>       File "<stdin>", line 1, in <module>
>     TypeError: unorderable types: int() < str()

What I meant is that you can't use a mixin to map __eq__ to __cmp__,
as you'll get TypeError even though == is defined for those types.

-- 
Adam Olsen, aka Rhamphoryncus