input: Write a python function to generate a list of items using a generator function.
  assert list(list_generator([2, 4, 6, 8])) == [2, 4, 6, 8]
  assert list(list_generator(['a', 'b', 'c'])) == ['a', 'b', 'c']
  assert list(list_generator([])) == []
output: def list_generator(items):
      for item in items:
          yield item