input: Write a function to find the union of two lists. The function should take two lists as input and return a set that contains all the unique elements from both lists.
  assert unionList([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])=={1, 2, 3, 4, 5, 6, 7}
  assert unionList([], [1, 2, 3])=={1, 2, 3}
  assert unionList([1, 2], [])=={1, 2}
  assert unionList([], [])==set()
output: def unionList(list1, list2):
      return set(list1).union(set(list2))