python，子进程:从子进程读取输出 [英] python, subprocess: reading output from subprocess

问题描述

我有以下脚本:

#!/usr/bin/python

while True:
    x = raw_input()
    print x[::-1]

我从 ipython 调用它:

In [5]: p = Popen('./script.py', stdin=PIPE)

In [6]: p.stdin.write('abc\n')
cba

它工作正常.

但是，当我这样做时:

In [7]: p = Popen('./script.py', stdin=PIPE, stdout=PIPE)

In [8]: p.stdin.write('abc\n')

In [9]: p.stdout.read()

解释器挂了.我究竟做错了什么?我希望能够多次写入和读取另一个进程，将一些任务传递给这个进程.我需要做什么不同的事情?

the interpreter hangs. What am I doing wrong? I would like to be able to both write and read from another process multiple times, to pass some tasks to this process. What do I need to do differently?

编辑 1

如果我使用 communicate，我会得到这个:

If I use communicate, I get this:

In [7]: p = Popen('./script.py', stdin=PIPE, stdout=PIPE)

In [8]: p.communicate('abc\n')
Traceback (most recent call last):
  File "./script.py", line 4, in <module>
    x = raw_input()
EOFError: EOF when reading a line
Out[8]: ('cba\n', None)

编辑 2

我试过冲洗:

#!/usr/bin/python

import sys

while True:
        x = raw_input()
        print x[::-1]
        sys.stdout.flush()

这里:

In [5]: from subprocess import PIPE, Popen

In [6]: p = Popen('./script.py', stdin=PIPE, stdout=PIPE)

In [7]: p.stdin.write('abc')

In [8]: p.stdin.flush()

In [9]: p.stdout.read()

但它又挂了.

推荐答案

我认为这里有两个问题:

I believe there are two problems at work here:

1) 您的父脚本调用 p.stdout.read()，它将读取所有数据，直到文件结束.但是，您的子脚本在无限循环中运行，因此文件结尾永远不会发生.可能你想要 p.stdout.readline()?

1) Your parent script calls p.stdout.read(), which will read all data until end-of-file. However, your child script runs in an infinite loop so end-of-file will never happen. Probably you want p.stdout.readline()?

2) 在交互模式下，大多数程序一次只缓冲一行.当从另一个程序运行时，它们会缓冲更多.缓冲在很多情况下提高了效率，但是当两个程序需要交互通信时就会出现问题.

2) In interactive mode, most programs do buffer only one line at a time. When run from another program, they buffer much more. The buffering improves efficiency in many cases, but causes problems when two programs need to communicate interactively.

在p.stdin.write('abc\n')之后添加:

p.stdin.flush()

在您的子进程脚本中，在 print x[::-1] 之后在循环中添加以下内容:

In your subprocess script, after print x[::-1] add the following within the loop:

sys.stdout.flush()

(和 import sys 在顶部)

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