input: 
  def print_unique(my_list):
      seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)
  """
  >>> print_unique([1, 2, 2, 3, 4, 4, 5])
  1
  2
  3
  4
  5
  """
  
output:     seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)