For example, I have two lists
A = [6, 7, 8, 9, 10, 11, 12] subset_of_A = [6, 9, 12]; # the subset of A the result should be [7, 8, 10, 11]; t
set(A)-set(subset_of_A) gives your the intended result set, but it won't retain the original order. The following is order preserving:
set(A)-set(subset_of_A)
[a for a in A if not a in subset_of_A]