python-3.x - 实时打印在 Python 中使用子进程启动的 bash 命令的结果

Question

我正在使用 subprocess 模块来运行 bash 命令。我想实时显示结果，包括没有添加新行但输出仍然被修改的情况。

我使用的是 python 3。我的代码使用子进程运行，但我对任何其他模块开放。我有一些代码可以为每添加一个新行返回一个生成器。

import subprocess
import shlex

def run(command):
    process = subprocess.Popen(shlex.split(command), stdout=subprocess.PIPE)
    while True:
        line = process.stdout.readline().rstrip()
        if not line:
            break
        yield line.decode('utf-8')

cmd = 'ls -al'
for l in run(cmd):
     print(l)   

例如，问题来自 rsync -P file.txt file2.txt 形式的命令，它显示一个进度条。

例如，我们可以从在 bash 中创建一个大文件开始:

base64 /dev/urandom | head -c 1000000000 > file.txt 

然后尝试用python显示rsync命令:

cmd = 'rsync -P file.txt file2.txt'
for l in run(cmd):
    print(l)

通过这段代码，只在进程结束时打印进度条，但我想实时打印进度。

Answer 1

来自 this answer你可以在 python 中打印时禁用缓冲:

You can skip buffering for a whole python process using "python -u" (or #!/usr/bin/env python -u etc) or by setting the environment variable PYTHONUNBUFFERED.

You could also replace sys.stdout with some other stream like wrapper which does a flush after every call.

Something like this (not really tested) might work...but there are probably problems that could pop up. For instance, I don't think it will work in IDLE, since sys.stdout is already replaced with some funny object there which doesn't like to be flushed. (This could be considered a bug in IDLE though.)

>>> class Unbuffered:
..     def __init__(self, stream):
..         self.stream = stream
..     def write(self, data):
..         self.stream.write(data)
..         self.stream.flush()
..     def __getattr__(self, attr):
..         return getattr(self.stream, attr)
..
>>> import sys
>>> sys.stdout=Unbuffered(sys.stdout)
>>> print 'Hello'
Hello