get text from rogramms runn by subprocess.Popen immediatetly

Rüdiger Ranft _rdi_ at web.de
Thu Apr 16 13:12:36 CEST 2009


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()

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