input: Write a function to remove duplicates from a list and return the list in the same order as the original elements appeared.
  
  def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))
  
  # Test cases
  assert remove_duplicates([1, 2, 3, 4, 3, 2, 1])==[1, 2, 3, 4]
  assert remove_duplicates([1, 1, 1, 1])==[1]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1, 2, 3, 4])==[1, 2, 3, 4]
  assert remove_duplicates([4, 3, 2, 1, 2, 3, 4])==[4, 3, 2, 1]
output: def remove_duplicates(my_list):
      seen = set()
      result = []
      for item in my_list:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result