input: Write a function to print the unique elements of a given list. If the list is empty, the function should not print anything.
  
  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, 3, 2, 1])==None
  assert print_unique([2, 4, 4, 6, 8, 8])==None
  assert print_unique([])==None
  assert print_unique([5])==None
  assert print_unique([3, 3, 3, 3])==None
output: def print_unique(my_list):
      seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)