input: Write a function to print the unique elements of a given list. If the list is empty, print nothing.
  def print_unique(my_list):
      seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)
  assert print_unique([1, 2, 2, 3, 4, 4]) == None
  assert print_unique([5, 5, 6, 7, 8, 8, 9]) == None
  assert print_unique([10, 11, 12, 12, 13]) == None
  assert print_unique([]) == None
output: def print_unique(my_list):
      seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)