Python - 从管道中简单的读取行
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Python - simple reading lines from a pipe
提问by Kiv
I'm trying to read lines from a pipe and process them, but I'm doing something silly and I can't figure out what. The producer is going to keep producing lines indefinitely, like this:
我试图从管道中读取行并处理它们，但我在做一些愚蠢的事情，我无法弄清楚是什么。生产者将无限期地保持生产线，如下所示：
producer.py
生产者.py
import time
while True:
print 'Data'
time.sleep(1)
The consumer just needs to check for lines periodically:
消费者只需要定期检查线路：
consumer.py
消费者.py
import sys, time
while True:
line = sys.stdin.readline()
if line:
print 'Got data:', line
else:
time.sleep(1)
When I run this in the Windows shell as python producer.py | python consumer.py, it just sleeps forever (never seems to get data?) It seems that maybe the problem is that the producer never terminates, since if I send a finite amount of data then it works fine.
当我在 Windows shell 中运行它时python producer.py | python consumer.py，它只是永远休眠（似乎永远不会获取数据？）似乎问题在于生产者永远不会终止，因为如果我发送有限数量的数据，那么它就可以正常工作。
How can I get the data to be received and show up for the consumer? In the real application, the producer is a C++ program I have no control over.
如何获取要接收的数据并显示给消费者？在实际应用中，生产者是一个我无法控制的C++程序。
采纳答案by Alex Martelli
Some old versions of Windows simulated pipes through files (so they were prone to such problems), but that hasn't been a problem in 10+ years. Try adding a
一些旧版本的 Windows 模拟管道通过文件（因此它们很容易出现此类问题），但这在 10 多年里都不是问题。尝试添加一个
sys.stdout.flush()
to the producer after the print, and also try to make the producer's stdout unbuffered (by using python -u).
之后到生产者print，并尝试使生产者的标准输出无缓冲（通过使用python -u）。
Of course this doesn't help if you have no control over the producer -- if it buffers too much of its output you're still going to wait a long time.
当然，如果您无法控制生产者，这将无济于事——如果它缓冲了太多的输出，您仍然会等待很长时间。
Unfortunately - while there are many approaches to solve that problem on Unix-like operating systems, such as pyexpect, pexpect, exscript, and paramiko, I doubt any of them works on Windows; if that's indeed the case, I'd try Cygwin, which puts enough of a Linux-like veneer on Windows as to often enable the use of Linux-like approaches on a Windows box.
不幸的是——虽然在类 Unix 操作系统上有很多方法可以解决这个问题，比如 pyexpect、pexpect、exscript和paramiko，但我怀疑它们中的任何一个都适用于 Windows；如果确实如此，我会尝试Cygwin，它在 Windows 上放置了足够的类似 Linux 的贴面，以便经常在 Windows 机器上使用类似 Linux 的方法。
回答by Nicolas Dumazet
This is about I/O that is bufferized by default with Python. Pass -uoption to the interpreter to disable this behavior:
这是关于默认使用 Python 缓冲的 I/O。将-u选项传递给解释器以禁用此行为：
python -u producer.py | python consumer.py
It fixes the problem for me.
它为我解决了问题。
