问题描述

我正在通过 Python 的子进程模块运行脚本.目前我使用:

I'm running a script via Python's subprocess module. Currently I use:

p = subprocess.Popen('/path/to/script', stdout=subprocess.PIPE, stderr=subprocess.PIPE)
result = p.communicate()

然后我将结果打印到标准输出.这一切都很好，但是由于脚本需要很长时间才能完成，所以我也希望从脚本实时输出到标准输出.我管道输出的原因是因为我想解析它.

I then print the result to the stdout. This is all fine but as the script takes a long time to complete, I wanted real time output from the script to stdout as well. The reason I pipe the output is because I want to parse it.

推荐答案

将子进程的标准输出保存到变量中以供进一步处理和 在子进程到达时运行时显示它:

To save subprocess' stdout to a variable for further processing and to display it while the child process is running as it arrives:

#!/usr/bin/env python3
from io import StringIO
from subprocess import Popen, PIPE

with Popen('/path/to/script', stdout=PIPE, bufsize=1,
           universal_newlines=True) as p, StringIO() as buf:
    for line in p.stdout:
        print(line, end='')
        buf.write(line)
    output = buf.getvalue()
rc = p.returncode

保存子进程的 stdout 和 stderr 更复杂，因为您应该同时使用两个流以避免死锁:

To save both subprocess's stdout and stderr is more complex because you should consume both streams concurrently to avoid a deadlock:

stdout_buf, stderr_buf = StringIO(), StringIO()
rc =  teed_call('/path/to/script', stdout=stdout_buf, stderr=stderr_buf,
                universal_newlines=True)
output = stdout_buf.getvalue()
...

teed_call() 在这里定义.

where teed_call() is define here.

更新:这里是一个更简单的asyncio版本.

^旧版本:

这是一个基于 child_process 的单线程解决方案.py 示例来自 tulip:

Here's a single-threaded solution based on child_process.py example from tulip:

import asyncio
import sys
from asyncio.subprocess import PIPE

@asyncio.coroutine
def read_and_display(*cmd):
    """Read cmd's stdout, stderr while displaying them as they arrive."""
    # start process
    process = yield from asyncio.create_subprocess_exec(*cmd,
            stdout=PIPE, stderr=PIPE)

    # read child's stdout/stderr concurrently
    stdout, stderr = [], [] # stderr, stdout buffers
    tasks = {
        asyncio.Task(process.stdout.readline()): (
            stdout, process.stdout, sys.stdout.buffer),
        asyncio.Task(process.stderr.readline()): (
            stderr, process.stderr, sys.stderr.buffer)}
    while tasks:
        done, pending = yield from asyncio.wait(tasks,
                return_when=asyncio.FIRST_COMPLETED)
        assert done
        for future in done:
            buf, stream, display = tasks.pop(future)
            line = future.result()
            if line: # not EOF
                buf.append(line)    # save for later
                display.write(line) # display in terminal
                # schedule to read the next line
                tasks[asyncio.Task(stream.readline())] = buf, stream, display

    # wait for the process to exit
    rc = yield from process.wait()
    return rc, b''.join(stdout), b''.join(stderr)

脚本运行 '/path/to/script 命令并同时逐行读取其标准输出和标准错误.这些行相应地打印到父级的 stdout/stderr 并保存为字节串以供将来处理.要运行 read_and_display() 协程，我们需要一个事件循环:

The script runs '/path/to/script command and reads line by line both its stdout&stderr concurrently. The lines are printed to parent's stdout/stderr correspondingly and saved as bytestrings for future processing. To run the read_and_display() coroutine, we need an event loop:

import os

if os.name == 'nt':
    loop = asyncio.ProactorEventLoop() # for subprocess' pipes on Windows
    asyncio.set_event_loop(loop)
else:
    loop = asyncio.get_event_loop()
try:
    rc, *output = loop.run_until_complete(read_and_display("/path/to/script"))
    if rc:
        sys.exit("child failed with '{}' exit code".format(rc))
finally:
    loop.close()

这篇关于将子进程输出显示到标准输出并重定向它的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！