docs: def _get_and_assert_slice_param(url_dict, param_name, default_int):
      """Return ``param_str`` converted to an int.
  
      If str cannot be converted to int or int is not zero or positive, raise
      InvalidRequest.
  
      """
      param_str = url_dict['query'].get(param_name, default_int)
      try:
          n = int(param_str)
      except ValueError:
          raise d1_common.types.exceptions.InvalidRequest(
              0,
              'Slice parameter is not a valid integer. {}="{}"'.format(
                  param_name, param_str
              ),
          )
      if n < 0:
          raise d1_common.types.exceptions.InvalidRequest(
              0,
              'Slice parameter cannot be a negative number. {}="{}"'.format(
                  param_name, param_str
              ),
          )
      return n