input: Write a python function to remove duplicate items from a list.
  assert remove_duplicates(['apple', 'pineapple', 'apple', 'banana']) == ['apple', 'pineapple', 'banana']
  assert remove_duplicates([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert remove_duplicates(['a', 'b', 'a', 'c', 'd', 'd']) == ['a', 'b', 'c', 'd']
output: def remove_duplicates(items):
      seen = set()
      result = []
      for item in items:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result