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