Python intersection and difference sum doesn't give me the actual number of the original set

Question

I have two lists, one with old IDs and one with new IDs.

I want to get items in common and items not common.

The new_Items list has all new ones. The old_It

Answer 1

A-B gives items of A which are not in B B-A gives items of B which are not in A Either of these is not what you are looking for

For items not common you need (A union B) minus (A intersection B) which is the symmetric difference of sets

You can also get by "(A-B) union (B-A)"