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).
--
Terry Jan Reedy
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