docs: def do_less_expensive_things(number):
      """
      Perform one expensive computation cooperatively with any
       other iterator passed into twisted's cooperate, then
       use it's result to pass into the second computation.
  
      :param number:
      :return:
      """
      result = yield batch_accumulate(1000, expensive(number))
      total = reduce(add, result, 0)
      log.msg("only for {}: {}".format(number, total))
      defer.returnValue(total)