从Python中的另一个进程实时拦截标准输出 [英] Real-time intercepting of stdout from another process in Python
问题描述
我想在Python脚本中逐行运行系统进程,截取输出并实时对其进行修改.
I'd like to run a system process, intercept the output, and modify it real-time, line by line, in a Python script.
我的最佳尝试是等待该过程在打印之前完成,
My best attempt, which waits for the process to complete before printing, is:
#!/usr/bin/env python
import subprocess
cmd = "waitsome.py"
proc = subprocess.Popen(cmd, shell=True, bufsize=256, stdout=subprocess.PIPE)
for line in proc.stdout:
print ">>> " + line.rstrip()
脚本waitsome.py
仅每半秒打印一行:
The script waitsome.py
simply prints a line every half a second:
#!/usr/bin/env python
import time
from sys import stdout
print "Starting"
for i in range(0,20):
time.sleep(0.5)
print "Hello, iteration", i
stdout.flush()
是否有一种简单的解决方案来获取subprocess
以允许实时迭代输出?我必须使用线程吗?
Is there an easy solution to get subprocess
to allow iterating over the output in real time? Do I have to use threads?
从前,我用Perl编写脚本,这真是小菜一碟:
Once upon a time, I scripted in Perl, and this was a piece of cake:
open(CMD, "waitsome.py |");
while (<CMD>) {
print ">>> $_";
}
close(CMD);
推荐答案
在文件上循环不可避免地将内容缓冲在很大的块中-这是所有Python 2. *实现的一个已知问题.它可以按照您在Python 3.1中的预期工作,最终循环略有不同:
Looping over a file unavoidably buffers things in pretty large chunks -- a known issue with all Python 2.* implementations. It works as you intend in Python 3.1, with the final loop being slightly different:
for line in proc.stdout:
print(">>> " + str(line.rstrip()))
如果升级到Python 3.1是不切实际的(并且我知道通常会这样!),请换一种方式,以老式的方式编写循环-以下版本的循环确实可以在Python中正常工作2.*:
If upgrading to Python 3.1 is impractical (and I know it will often be!), go the other way and write the loop in an old-fashioned manner -- the following version of the loop does work as you intend in Python 2.*:
while True:
line = proc.stdout.readline()
if not line:
break
print ">>> " + line.rstrip()
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