Hundreds of people want an orderedset ( and yet the ordered sets that are in PyPI (oset, ordered-set) are incomplete.  Please consider adding an ordered set that has *all* of the same functionality as set.

The only major design decision is (I think) whether to store the elements in a linked list or dynamic vector.

My personal preference is to specify the ordered set via a flag to the constructor, which can be intercepted by __new__ to return a different object type as necessary.

(If anyone wants to add a complete ordered set to PyPI that would also be very useful for me!)