Python:在后台进程上使用popen poll [英] Python: Using popen poll on background process

问题描述

我正在后台运行一个很长的进程(实际上是另一个python脚本).我需要知道什么时候结束.我发现Popen.poll()对于后台进程总是返回0.还有另一种方法吗?

I am running a long process (actually another python script) in the background. I need to know when it has finished. I have found that Popen.poll() always returns 0 for a background process. Is there another way to do this?

p = subprocess.Popen("sleep 30 &", shell=True,
    stdout=subprocess.PIPE, stderr=subprocess.PIPE)
a = p.poll()
print(a)

以上代码从不打印None.

推荐答案

您无需使用shell后台&语法，因为subprocess会自行在后台运行该进程

You don't need to use the shell backgrounding & syntax, as subprocess will run the process in the background by itself

只需正常运行命令，然后等待Popen.poll返回not None

Just run the command normally, then wait until Popen.poll returns not None

import time
import subprocess

p = subprocess.Popen("sleep 30", shell=True)
# Better: p = subprocess.Popen(["sleep", "30"])

# Wait until process terminates
while p.poll() is None:
    time.sleep(0.5)

# It's done
print "Process ended, ret code:", p.returncode

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