code: def not_right(self, num):
          
          if not self.list:
              self._build_list()
  
          if num == None:
              return self.list[:-1:]
          if num <= 0:
              return []
  
          return self.list[:-num:]
docs: WITH SLICES BEING FLAT, WE NEED A SIMPLE WAY TO SLICE FROM THE LEFT [:-num:]