Ian Simcock wrote:
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?
I have tried your code with "ping google.com" as command and got the
same results; apparently something buffers the output. The result is
different when using Python 3.3: there, the lines are printed as they
come in. This seems to indicate a bug in the Python 2.7 implementation.
There are some bug reports on bugs.python.org that may be related; see
for example:
http://bugs.python.org/issue15532
I have been playing around a bit with the suggested approach of using
the io library directly. I managed to get unbuffered output, but
unfortunately the program hangs when the subprocess is done. It can't
even be terminated with Control-C, I have to use task manager to kill
python.exe.
Below is as far as I got; perhaps someone with more experience with
pipes knows how to fix this.
Regards,
Gertjan.
#!/usr/bin/env python2.7
# coding: CP1252
from __future__ import print_function
import subprocess
import io, os
def main():
i, o = os.pipe()
piperead = io.open(i, 'rb', buffering=1)
p = subprocess.Popen(["ping", "google.com"],
stdout=o,
stderr=subprocess.PIPE,
bufsize=0,
shell=False)
for line in piperead:
print(line)
if __name__ == '__main__':
main()
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