You could create such a class with a few lines of code by inheriting from

collections.abc.MutableSet

You as anyone with a pontual problem that would benefit from such a construct -

I can't see why/when this would be useful unless in a project already dealing

with symbolic/lazy mathematical concepts - in which case, the author would

be already aware of these possibilities.

On Mon, 10 Aug 2020 at 08:23, haael <haael@interia.pl> wrote:

Forgive me if this has already been discussed.

Could we add the idea of "negative" sets to Python? That means sets that
contain EVERYTHING EXCEPT certain elements.

First, let's have a universal set that contains everything.

assert element in set.UNIVERSAL

The universal set is a superset of every other set.

assert set.UNIVERSAL >= any_set

Adding anything to universal set doesn't change anything.

assert set.UNIVERSAL | element == set.UNIVERSAL

However REMOVING an element from the set puts it on "negative list".

myset = set.UNIVERSAL
myset.remove(element)
assert element not in myset

Intersection of a "negative set" with a normal set gives again a normal
set. Union of two negative sets, or a negative set with a normal set,
gives a negative set.

The main issue: negative sets would not be iterable, but you can
intersect them with the desired subdomain and iterate over.
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