[Python-3000] Total ordering and __cmp__

[Guido van Rossum]

On 3/21/07, Georg Brandl <g.brandl at gmx.net> wrote:
> Terry Reedy schrieb:
> > "Georg Brandl" <g.brandl at gmx.net> wrote in message
> > news:etrj1a$l9a$1 at sea.gmane.org...
> > | Yes, but dictionaries had an explicit ordering in dict_compare() which
> > was
> > | deleted.
> >
> > Is dict_compare something added in 2.5?  It is neither a builtin or dict
> > method in 2.4.
>
> No, it is a C function in dictobject.c, in Python available as dict.__cmp__.
>
> > In any case, this point is that dict ordering is as arbitrary as ordering,
> > for instance, a dict and a string.  Since Guido stopped the experiment of
> > totally ordering all objects when complex nums were added, consistency
> > suggests that all fake orderings be eliminated, leaving only the order of
> > numbers, characters, and sequences of comparable objects.
>
> It was not really *that* arbitrary. There was a defined algorithm, and it
> made some sense (at least for 1-item-dicts).

It was well-defined because I had to do *something* that depended only
on the keys and values and not on object identities etc. I never
considered it *userful* and I don't know of anyone who used it.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)