在子进程运行时拦截它的stdout [英] Intercepting stdout of a subprocess while it is running
问题描述
如果这是我的子流程:
import time, sys
for i in range(200):
sys.stdout.write( 'reading %i\n'%i )
time.sleep(.02)
这是控制和修改子流程输出的脚本:
And this is the script controlling and modifying the output of the subprocess:
import subprocess, time, sys
print 'starting'
proc = subprocess.Popen(
'c:/test_apps/testcr.py',
shell=True,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE )
print 'process created'
while True:
#next_line = proc.communicate()[0]
next_line = proc.stdout.readline()
if next_line == '' and proc.poll() != None:
break
sys.stdout.write(next_line)
sys.stdout.flush()
print 'done'
为什么readline
和communicate
等到进程完成运行?是否有一种简单的方法可以实时传递(和修改)子进程的stdout?
Why is readline
and communicate
waiting until the process is done running? Is there a simple way to pass (and modify) the subprocess' stdout real-time?
顺便说一句,我已经看过此,但我不需要日志记录功能(也不必担心太多).
BTW, I've seen this, but I don't need the logging features (and havn't bothered understand much of it).
我在Windows XP上.
I'm on Windows XP.
推荐答案
正如查尔斯已经提到的那样,问题出在缓冲中.在为SNMPd编写一些模块时遇到了类似的问题,并通过用自动刷新版本替换stdout来解决了该问题.
As Charles already mentioned, the problem is buffering. I ran in to a similar problem when writing some modules for SNMPd, and solved it by replacing stdout with an auto-flushing version.
我使用了以下代码,这些代码受ActiveState上的一些帖子启发:
I used the following code, inspired by some posts on ActiveState:
class FlushFile(object):
"""Write-only flushing wrapper for file-type objects."""
def __init__(self, f):
self.f = f
def write(self, x):
self.f.write(x)
self.f.flush()
# Replace stdout with an automatically flushing version
sys.stdout = FlushFile(sys.__stdout__)
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