Question

我正在通过Python的子进程模块运行脚本。目前我使用：

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。这很好，但由于脚本需要很长时间才能完成，我还希望从脚本到stdout的实时输出。我输出输出的原因是因为我想解析它。

Answer 1

保存子流程＆＃39; stdout到变量进行进一步处理和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

要保存子流程的stdout和stderr更复杂，因为你应该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()
...

其中teed_call() is define here。

更新：此处a simpler asyncio version。

^旧版本：

这是基于child_process.py example from tulip的单线程解决方案：

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stdout和stderr。这些行相应地打印到父级stdout / stderr并保存为字节串以供将来处理。要运行read_and_display()协同程序，我们需要一个事件循环：

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()

Answer 2

p.communicate() waits for the subprocess to complete然后立即返回其整个输出。

您是否尝试过类似的东西，在那里逐行读取子进程输出？

p = subprocess.Popen('/path/to/script', stdout=subprocess.PIPE, stderr=subprocess.PIPE)
for line in p.stdout:
  # do something with this individual line
  print line

Answer 3

Popen.communicate文件明确指出：

Note: The data read is buffered in memory, so do not use this method if the data size is large or unlimited.

https://docs.python.org/2/library/subprocess.html#subprocess.Popen.communicate

因此，如果您需要实时输出，则需要使用以下内容：

stream_p = subprocess.Popen('/path/to/script', stdout=subprocess.PIPE, stderr=subprocess.PIPE)

while stream_line in stream_p:
    #Parse it the way you want
    print stream_line

Answer 4

这会将stdout和stderr都打印到终端，并将stdout和stderr都保存到变量中：

from subprocess import Popen, PIPE, STDOUT

with Popen(args, stdout=PIPE, stderr=STDOUT, text=True, bufsize=1) as p:
    output = "".join([print(buf, end="") or buf for buf in p.stdout])

但是，根据您的实际操作，可能需要注意以下几点：通过使用stderr=STDOUT，我们无法再区分stdout和stderr了，而通过调用print，您的输出将始终打印到stdout，无论它来自stdout还是stderr。

对于Python <3.7，您将需要使用universal_newlines而不是text。

版本3.7中的新增功能：已添加文本作为Universal_newlines的易读别名。

来源：https://docs.python.org/3/library/subprocess.html#subprocess.Popen

将子进程输出显示到stdout并重定向它

4 个答案: