> On 8 Apr 2019, at 19:37, Terry Reedy <tjre...@udel.edu> wrote:
>
> On 4/8/2019 5:40 AM, Steven D'Aprano wrote:
>> On Mon, Apr 08, 2019 at 07:44:41AM +0100, Alex Chamberlain wrote:
>>> I think a better abstraction for a sorted list is a new class, which
>>> implements the Sequence protocol (and hence can be used in a lot of
>>> existing list contexts), but only exposed mutation methods that can
>>> guarantee that sorted order can be maintained
>> Perhaps that's a better idea.
>>> (and hence is _not_ a MutableSequence).
>> Right, but it can still be mutable, so long as the mutation methods can
>> maintain the invariant. That means:
>> - the SortedList needs to know the sort direction;
>> - and the key used for sorting;
>> - no slice or item assignment;
>
> Item assignment could be allowed if it checked the new value against
> neighbors and raised ValueError if it would 'unsort' the list.
>> - insertions are okay, since the SortedList can put them in
>> the correct place;
>> - but not append;
>> - deletions are okay, since they won't change the sort invariant
>> (at least not for items with a total order).
How do you handle a list of objects that after insertion and being sorted
change their sort key and thus make the list unsorted.
>From the point of view of the list nothing changed, but its not sorted now.
Think if a list of file stat info objects that are sorted by size.
As the files are written to the size changes.
I can loop over the objects and tell them to update the stats.
Now the __is_sorted__ property is wrong.
Barry
>
>
> --
> Terry Jan Reedy
>
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