关于ＡＣＭ的A + B Problem的示列

[Ray_20]

#! /usr/bin/python
#coding=utf-8

from sys import stdin
for line in stdin:
    a = line.split()
    print int(a[0]) + int(a[1])

inlist = raw_input().split()
print sum(int(inlist[i]) for i in range(2))

为何一定要用stdin才行，下面这种方法不行么？蛋疼