On Mon, Apr 08, 2019 at 03:18:53PM +1000, Cameron Simpson wrote:
> If this is a publicly queriable value, is there any need to have a
> dunder name at all? Why not just give lists a public is_sorted
> attribute?
I don't mind that.
> I'm also not convinced the cost to every insert/append is worth the
> (subjectively to me) highly infrequent use.
>
> I imagine one could increase the utility of the flag by implementing
> insert/append with a bit of logic like:
>
> if self.__issorted__:
> check-previous/next elements to see if sortedness is preserved
That's not practical unless the list remembers what sort of sort order
it is supposed to have:
- sorted smallest to biggest;
- or biggest to smallest;
- using what key.
That might be appropriate for a dedicated SortedList class, but not for
generic lists. But a SortedList class probably shouldn't support
operations which break the sorted invariant.
> Conjecture: anything that requires a sorted list but _accepts_ an
> unsorted list (eg outer code which uses bisect or median) needs to check
> for sortedness and sort if not already sorted.
Well, yes, somebody has to sort the list at least once, otherwise it
won't be sorted :-)
Currently bisect simply trusts that the list is sorted and makes no
effort to even check. The API basically says:
Pass a sorted list, or you'll get garbage.
With this check in place, it is *possible* to change the API to:
Pass a sorted list, or I'll sort it for you; if you lie,
you'll get garbage.
(Whether the maintainer of bisect thinks this is a good API change, I
don't know.)
The median (and soon, quantiles) API says:
I'm going to sort the list for you, whether you need it or
not, just in case you do.
It could become:
I'm going to sort the list for you, if necessary. If you
lie about it already being sorted, you'll get garbage.
--
Steven
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