input: Write a function to print the unique elements of a given list.
  assert print_unique([1, 2, 2, 3, 4, 4, 5])==None
  assert print_unique([5, 5, 5, 5])==None
  assert print_unique([])==None
output: def print_unique(lst):
      unique_elements = list(set(lst))
      for element in unique_elements:
          print(element)