input: Write a python function to return unique elements from a list in the order they first appear.
  assert get_unique([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert get_unique([10, 20, 20, 30, 40, 40, 50]) == [10, 20, 30, 40, 50]
  assert get_unique([5, 5, 7, 7, 9, 9, 8, 8, 6, 6, 4, 4, 3, 3]) == [5, 7, 9, 8, 6, 4, 3]
output: def get_unique(lst):
      seen = set()
      unique_list = []
      for item in lst:
          if item not in seen:
              unique_list.append(item)
              seen.add(item)
      return unique_list