[Python-ideas] Exploiting type-homogeneity in list.sort() (again!)

[Elliot Gorokhovsky]

On Tue, Mar 7, 2017 at 1:47 PM Erik <python at lucidity.plus.com> wrote:

>
> I'd prefer the sort optimization to be based on what my list contains
> NOW, not on what it may have contained some time in the past, so I'm not
> a fan of the "once heterogeneous, always considered heterogeneous"
> behaviour if it's cheap enough to avoid it.
>

Sure. Dictionaries actually don't implement this, though: as soon as they
see a non-string key, they permanently switch to a heterogeneous state
(IIRC).

I think the bigger problem, though, is that most list use does *not*
involve sorting, so it would be a shame to impose the non-trivial overhead
of type-checking on *all* list use. With dictionaries, you have to
type-check inserts anyway (for equality testing), so it's less of a
problem.  But the fundamental list operations *don't* require type-checking
currently, so why add it in? In practice, the pre-sort check is *very*
cheap, and its cost is only imposed on sort usage.

Anyway, my patch could always be a precursor to a more general optimization
along these lines. I'm almost finished fixing the problem Tim identified
earlier in this thread; after that, it'll be ready for review!
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