python中subprocess.Popen.poll

import subprocess

proc = subprocess.Popen(['python', 'test.py'], stdout=subprocess.PIPE)

while 1:
    print proc.poll() 

#while 1:
#     print "hello"

print "hello"

测试代码如上，poll函数返回码：

0 正常结束

1 sleep

2 子进程不存在

-15 kill

None 在运行

poll的返回： A None value indicates that the process hasn’t terminated yet.A negative value -N indicates that the child was terminated by signal N (Unix only).

ps：=====================================================================================================

self.proc.poll() == 0 判断子进程是否正常结束 正确
self.proc.poll() <= 0 会导致进程在一段时间内没有上报状态 具体原因？？？ 有问题

self.proc.poll() is not  None判断进行是否结束