input: Write a function to remove duplicates from a list. Return the list with all duplicates removed. If the list is empty, 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, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
output: def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))