code: def make_slice_key(cls, start_string, size_string):
          
          try:
              start = int(start_string)
          except ValueError:
              raise ValueError('Query parameter "start" must be a number.')
          if start < 0:
              raise ValueError('Query parameter "start" must be zero or '
                               'a positive number.')
          try:
              size = int(size_string)
          except ValueError:
              raise ValueError('Query parameter "size" must be a number.')
          if size < 1:
              raise ValueError('Query parameter "size" must be a positive '
                               'number.')
          return slice(start, start + size)
docs: Converts the given start and size query parts to a slice key.
  
          :return: slice key
          :rtype: slice