[Python-Dev] Re: Re: lists v. tuples
Aahz
aahz@pythoncraft.com
Sun, 16 Mar 2003 10:37:14 -0500
On Sun, Mar 16, 2003, Guido van Rossum wrote:
>
> I realized the first sentence wasn't very clear. I meant that
> implementing cmp() is inefficient without __cmp__ for some types
> (especially container types). Example:
>
> cmp(range(1000)+[1], range(1000)+[0])
>
> If the list type implements __cmp__, each of the pairs of items is
> compared once. OTOH, if the list type only implemented __lt__, __eq__
> and __gt__, cmp() presumably would have to try one of those first, and
> then another one. If it picked __lt__ followed by __eq__, it would
> get two False results in a row, meaning it could return 1 (cmp()
> doesn't really expect incomparable results :-), but at the cost of
> comparing each pair of items twice. If cmp() picked another set of
> two operators to try, I'd simply adjust the example.
That's something I've been thinking about. I use cmp() for that purpose
in the BCD module, because I do need the 3-way result (and it appears
that Eric kept that). OTOH, it's certainly easy enough to define a
cmp() function, and not having the builtin wouldn't kill performance.
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