get text from rogramms runn by subprocess.Popen immediatetly

norseman norseman at hughes.net
Thu Apr 16 20:13:13 CEST 2009


Rüdiger Ranft wrote:
> Hi all,
> 
> I need to call some programms and catch their stdout and stderr streams.
> While the Popen class from subprocess handles the call, I get the
> results of the programm not until the programm finishes. Since the
> output of the programm is used to generate a progress indicator, I need
> a way to acces the values written to stdout/stderr as fast as possible.
> 
> Beneath is a test which shows what I did
> 
> TIA
> Rudi
> 
> ----8<-------8<-------8<-- iodummy.cpp -8<-------8<---
> #include <iostream>
> #include <unistd.h>
> 
> int main()
> {
>         for( int i = 0; i < 10; i++ )
>         {
>                 std::cerr << i << std::endl;
>                 sleep(2);
>         }
> }
> 
> from subprocess import Popen, PIPE
> from time import sleep
> 
> p = Popen('./iodummy',stdin=PIPE, stdout=PIPE, stderr=PIPE)
> sleep(3)
> # now I expect '0\n1\n' in stderr, but read() blocks until
> # the end of iodummy.
> print p.stderr.read()
> p.wait()
> 
> 
> 
> ------------------------------------------------------------------------
> 
> --
> http://mail.python.org/mailman/listinfo/python-list
========================
Take a look at lib.pdf section 14.1.2  popen3
avoids PIPE problems


Steve



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