setlist

A setlist is an ordered, indexed collection with unique elements. The class implements Sequence and Set and should be able to be used as a drop in replacement for a set or list of you want to add the add an additional constraint of ordering or uniqueness. It it more than just an ordered Set in that the elements are accessible by index (ie. not just a linked set).

However, setlist‘s are not comparable like sets or lists. Equality testing still works, but setlist(('a', 'c')) < setlist(('a', 'b')) does not because we’d have to choose to compare by order or by set comparison.

Differences from list

• Inclusion testing is O(1)
• Adding an element that is already present does nothing

Differences from set

• Elements are ordered and accessible by index
• Adding an element is O(n) as opposed to O(1)

New Methods

Aside from the methods expected from Sequence and Set, this provides: - setlist.shuffle(random=None)

Because random.shuffle(setlist) doesn’t work, this is provided to do the same.

Quirks

• Swapping elements, eg. sl[0], sl[1] = sl[1], sl[0], doesn’t work because it is implemented by first inserting one element then the other. But since the first element it tries to insert is still in the setlist, nothing happens. This causes random.shuffle not to work on a setlist.