input: Write a function to print the unique elements of a given list. The function should iterate through the list, printing each element only once. If the list is empty, it should 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])==None
  assert print_unique([10, 20, 30, 20, 10])==None
  assert print_unique([5, 5, 5, 5])==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)