Subprocess.Popen 在解释器、可执行脚本中的行为不同 [英] Subprocess.Popen behaves differently in interpreter, executable scripts

问题描述

假设您有以下内容:

command = shlex.split("mcf -o -q -e -w %s %s" % (SOLFILE, NETFILE))任务 = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)标准输出，标准错误 = task.communicate()打印 "stdout: %s" % stdout #debugging打印 "stderr: %s" % stderr #debugging如果标准错误:sys.exit("MCF 在 %s 上崩溃" % NETFILE)

没有必要知道 mcf 是什么，除非它是一个 C 程序，如果没有提供可满足的网络文件，它将溢出.(为什么我不能确保所有的网络文件都可以满足?好吧，因为检查它的最简单方法是将它提供给 mcf 并查看它是否溢出......)

无论如何，当我在可执行脚本中运行它时，task.communicate() 似乎没有在 stdout 和 stderr 中存储任何内容.(准确地说，我得到 stdout == stderr == ''.)相反，来自 mcf 的 stderr 流似乎泄漏"到终端，而不是被子进程管道捕获.下面是一些示例输出来说明:

网络文件:facility3cat_nat5000_wholesaler_capacitation_test_.netSolfile:facilities3cat_nat5000_wholesaler_capaitation_test_.sol*** 检测到缓冲区溢出 ***:mcf 已终止======== 回溯:==========......[五十行琳达布莱尔式的输出]......标准输出:无标准错误:...[程序继续，因为 stderr 没有评估为 True] ...

这只会在从命令行运行脚本时失败.当我在解释器中逐行执行时，正确分配了 stdout 和 stderr:

<预><代码>>>>任务 = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)>>>标准输出，标准错误 = task.communicate()>>>标准错误'*** 检测到缓冲区溢出 ***:mcf 终止\n======== 回溯:==========\n'... [更多的头晕和呕吐] ...

谁能帮助我理解为什么这在解释器中有效，但在执行时无效?提前致谢！

解决方案

我写了一个小测试脚本来测试 subprocess 模块.

#!/bin/bashecho echo to stderr 1>&2回显到标准输出

然后我写了一个小的 Python 脚本来调用它:

#!/usr/bin/python导入子流程命令 = ('./joe.sh',)任务 = subprocess.Popen(command, stdout=subprocess.PIPE,stderr=subprocess.PIPE)标准输出，标准错误 = task.communicate()打印 'stdout == %r\nstderr == %r' % (stdout, stderr)

运行结果如下:

$ python joe.pystdout == 'echo to stdout\n'stderr == 'echo to stderr\n'

在 ipython 中运行相同序列的输出是相同的.

所以 subprocess 模块的行为方式符合您的预期，而不是您的问题中的行为方式.我认为除了 subprocess 模块之外的其他东西一定有问题，因为你所做的对我有用.

我正在运行 Python 2.7，所以另一种可能是 subprocess 模块的旧版本中可能存在某种奇怪的错误.

Let's say you have the following:

command = shlex.split("mcf -o -q -e -w %s %s" % (SOLFILE, NETFILE))
task = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = task.communicate()
print "stdout: %s" % stdout #debugging
print "stderr: %s" % stderr #debugging
if stderr:
    sys.exit("MCF crashed on %s" % NETFILE)

It's not necessary to know what mcf is, except that it's a C program which will overflow if it's not given a satisfiable netfile. (Why can't I just ensure that all the netfiles are satisfiable? Well, because the easiest way to check that is to feed it to mcf and see if it overflows...)

Anyway, when I run this in an executable script, task.communicate() doesn't seem to store anything in stdout and stderr. (To be precise, I get stdout == stderr == ''.) Instead, the stderr stream from mcf seems to be "leaking" to the terminal rather than getting captured by the subprocess pipe. Here's some sample output to illustrate:

Netfile: facility3cat_nat5000_wholesaler_capacitation_test_.net
Solfile: facility3cat_nat5000_wholesaler_capacitation_test_.sol
*** buffer overflow detected ***: mcf terminated
======= Backtrace: =========
...
...[fifty lines of Linda Blair-esque output]...
...
stdout: None
stderr: 
...[program continues, since stderr did not evaluate to True]...

This only fails when running the script from the command line. When I step through it line by line in the interpreter, stdout and stderr are correctly assigned:

>>> task = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>> stdout, stderr = task.communicate()
>>> stderr
'*** buffer overflow detected ***: mcf terminated\n======= Backtrace: =========\n'
...[more headspinning and vomit]...

Could anyone help me to understand why this works in the interpreter, but not when executed? Thanks in advance!

解决方案

I wrote a little test script to test the subprocess module with.

#!/bin/bash

echo echo to stderr 1>&2
echo echo to stdout

Then I wrote a small Python script that calls it:

#!/usr/bin/python

import subprocess

command = ('./joe.sh',)
task = subprocess.Popen(command, stdout=subprocess.PIPE,
                                 stderr=subprocess.PIPE)
stdout, stderr = task.communicate()
print 'stdout == %r\nstderr == %r' % (stdout, stderr)

The output of running it looks just like this:

$ python joe.py 
stdout == 'echo to stdout\n'
stderr == 'echo to stderr\n'

The output of running that same sequence in ipython is the same.

So the subprocess module is behaving in the manner you expect, and not how it's behaving for you in your question. I think something other than the subprocess module must be at fault here because what you're doing works for me.

I'm running Python 2.7, so another possibility is that maybe there is some kind of weird bug in older versions of the subprocess module.

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