input: Write a function to remove duplicates from a list and return the modified list. The function should maintain the original order of elements as they first appear in the input list. If the input list is empty, the function should return an empty list.
  def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))
  
  assert remove_duplicates([1, 2, 3, 4, 3, 2, 1]) == [1, 2, 3, 4]
  assert remove_duplicates([5, 5, 5, 5]) == [5]
  assert remove_duplicates([]) == []
  assert remove_duplicates([1, 1, 2, 2, 3, 3, 4, 4]) == [1, 2, 3, 4]
  assert remove_duplicates([7, 8, 9, 7, 8, 9]) == [7, 8, 9]
output: def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))