Path: csiph.com!usenet.pasdenom.info!news.etla.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Date: Fri, 23 Aug 2013 11:53:13 +0200
From: Antoon Pardon <antoon.pardon@rece.vub.ac.be>
User-Agent: Mozilla/5.0 (X11; Linux i686; rv:10.0.12) Gecko/20130116 Icedove/10.0.12
MIME-Version: 1.0
To: python-list@python.org
Subject: Re: Running a command line program and reading the result as it runs
References: <5215a6cf$0$6512$c3e8da3$5496439d@news.astraweb.com>
In-Reply-To: <5215a6cf$0$6512$c3e8da3$5496439d@news.astraweb.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.158.1377251601.19984.python-list@python.org>
Lines: 52
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:52875

Op 22-08-13 07:51, Ian Simcock schreef:
> Greetings all.
> 
> I'm using Python 2.7 under Windows and am trying to run a command line
> program and process the programs output as it is running. A number of
> web searches have indicated that the following code would work.
> 
> import subprocess
> 
> p = subprocess.Popen("D:\Python\Python27\Scripts\pip.exe list -o",
>                      stdout=subprocess.PIPE,
>                      stderr=subprocess.STDOUT,
>                      bufsize=1,
>                      universal_newlines=True,
>                      shell=False)
> for line in p.stdout:
>     print line
> 
> When I use this code I can see that the Popen works, any code between
> the Popen and the for will run straight away, but as soon as it gets to
> the for and tries to read p.stdout the code blocks until the command
> line program completes, then all of the lines are returned.
> 
> Does anyone know how to get the results of the program without it blocking?

Maybe the following can work?

Untested code:

from pty import openpty
from subprocess import Popen

master, slave = openpty()

p = Popen("D:\Python\Python27\Scripts\pip.exe list -o",
          stdout = slave,
          stderr = slave,
          stdin = slave,
          close_fds = True)

for line in master:
    print line


The idea is to set a a pseudo terminal for pip so that the
system thinks pip is doing IO with a terminal and so the
IO will be line buffered. But all IO from pip will be available
through the master in your program.

-- 
Antoon Pardon