input: Write a function to print the unique elements of a given list. Use a set to keep track of elements that have already been seen and print each element only once.
  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([3, 4, 5, 1, 2, 4, 2])
  assert print_unique([3, 5, 10, 1, 2, 10])
  assert print_unique([4, 3, 1, 2, 3])
  assert print_unique([3, 5, 4, 1, 2])
  assert print_unique([])
output: def print_unique(my_list):
      seen = set()
      for x in my_list:
          if x not in seen:
              print(x)
              seen.add(x)