test = set([1, 2, 3]);

>>> a = {1, 2, 3, 4}
>>> b = {3, 4, 5, 6}
>>> print a.union(b)
set([1, 2, 3, 4, 5, 6])

>>> l1 = [1, 2, 3]
>>> l2 = [2, 4, 3]
>>> print set(l1).intersection(l2)
set([2, 3])