input: Write a function to print the unique elements of a given list.
  
  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])
  assert print_unique(['a', 'b', 'b', 'c', 'c', 'c'])
  assert print_unique([])
  assert print_unique([5, 5, 5, 5, 5])
output: def print_unique(my_list):
      seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)