input: Write a function to remove duplicates from a 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, 6, 7, 5, 7, 6])==[5, 6, 7]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1, 1, 1, 1, 1])==[1]
  assert remove_duplicates([2, 2, 3, 3, 4, 4])==[2, 3, 4]
output: def remove_duplicates(my_list):
      return list(dict.fromkeys(my_list))