input: 
  def unionList(list1, list2):
      """
      Find the union of two lists.
      >>> unionList([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])
      {1, 2, 3, 4, 5, 6, 7}
      """
      return set(list1 + list2)
  
output:     union_set = set(list1).union(set(list2))
      return union_set