python script hangs when run from subprocess

[Larry.Martell at gmail.com]

On Saturday, September 7, 2013 5:19:25 AM UTC-6, Peter Otten wrote:
> Larry.Martell at gmail.com wrote:
> 
> 
> 
> > I have a python script and when I run it directly from the command line it
> 
> > runs to completion. But I need to run it from another script. I do that
> 
> > like this:
> 
> > 
> 
> > p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
> 
> > stderr=subprocess.STDOUT) rv = p.wait()
> 
> > out_buf = p.stdout.read()
> 
> > 
> 
> > When I do this, wait never returns. If I trace the underlying script it's
> 
> > always in the same write to stderr that never seems to complete:
> 
> > 
> 
> > write(2, "/KA22/05Feb12/Images/12063LBO003"..., 24457
> 
> > 
> 
> > I run many other scripts and commands in the same manner, and they all
> 
> > complete, it's just this one. Anyone have any ideas why this is happening,
> 
> > and how I can further debug or fix this?
> 
> 
> 
> The script writes to an OS buffer, and when that buffer is full it blocks 
> 
> forever. p.wait() in turn then waits forever for the script to terminate...
> 
> 
> 
> As a fix try
> 
> 
> 
> out_buf = subprocess.Popen(...).communicate()[0]
> 
> 
> 
> 
> 
> This uses threads or select (depending on the OS) to avoid the problem -- 
> 
> and is prominently mentionend in the documentation:
> 
> 
> 
> http://docs.python.org/2/library/subprocess.html#subprocess.Popen.wait

Thanks. I hadn't seen this. I'll check it out.