input: Write a function to remove duplicates from a list and return the list with unique elements in the order they first appeared.
  def remove_duplicates(my_list):
   return list(dict.fromkeys(my_list))
  
  my_list = [1, 2, 3, 4, 3, 2, 1]
  assert remove_duplicates(my_list) == [1, 2, 3, 4]
  
  my_list = [5, 5, 5, 5, 5]
  assert remove_duplicates(my_list) == [5]
  
  my_list = []
  assert remove_duplicates(my_list) == []
  
  my_list = [1, 1, 2, 2, 3, 3]
  assert remove_duplicates(my_list) == [1, 2, 3]
output: def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))