input: Write a function to print the unique elements of a given list. 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(["a", "b", "c", "a"])==None
  assert print_unique([1, 2, 2, 3])==None
  assert print_unique(["apple", "banana", "apple", "cherry"])==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)