Problems with os.system

[alexLIGO]

Hi,

I am trying to run a python script that executes several other programs
on the bash (under linux) and reads some of the output of those
programs. This works fine for a couple of os.system() calls, but then
it does not work anymore. os.system() returns always -1, but when
executing exactly the same program directly on the linux-bash it works!

Could this be a memory problem? It happens when there is much data
stored in a python list. How can I check the memory usage in my python
script? Can I force python to execute the program on the bash? What can
I do?

I would very appreciate help in that.

Alexander

[marduk]

On Fri, 2005-09-02 at 13:45 -0700, alexLIGO wrote:

Hi,

I am trying to run a python script that executes several other programs
on the bash (under linux) and reads some of the output of those
programs. This works fine for a couple of os.system() calls, but then
it does not work anymore. os.system() returns always -1, but when
executing exactly the same program directly on the linux-bash it works!

Could this be a memory problem? It happens when there is much data
stored in a python list. How can I check the memory usage in my python
script? Can I force python to execute the program on the bash? What can
I do?

Are you trying to read the output (stdout) of the program? If so you
should be using os.popen() not os.system().

[alexLIGO]

No I read some other data files that has been created by the other
program. I am not interested in the stdout or err of that program...

[Michael Hoffman]

alexLIGO wrote:

I am trying to run a python script that executes several other programs
on the bash (under linux) and reads some of the output of those
programs. This works fine for a couple of os.system() calls, but then
it does not work anymore. os.system() returns always -1, but when
executing exactly the same program directly on the linux-bash it works!
Try to break this down to a minimal testcase and then post that.

Also, I usually use the subprocess module instead of os.system these days.
How can I check the memory usage in my python
script? Can I force python to execute the program on the bash?

If bash is your shell, then os.system will call the program through a
bash subshell.
--
Michael Hoffman

[jepler]

Repeated calls to system() seem to cause no problem here.

I ran the following program:
import os

for i in xrange(10000):
assert os.system("true ") == 0
in around 25 seconds, the 'for' loop completed, and the 'true' command
always returned 0 from system, as expected.

Jeff

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[jepler]

On Fri, Sep 02, 2005 at 01:45:42PM -0700, alexLIGO wrote:

Can I force python to execute the program on the bash? What can
I do?

os.system() is a wrapper on system(3), which invokes /bin/sh.

If you want to use a different shell, you can use
os.spawnv(os.P_ WAIT, '/bin/bash', ['bash', '-c', command])
or even avoid the use of a shell altogether:
os.spawnvp(os.P _WAIT, 'myprogram', ['myprogram', '-arg1', 'arg2'])

Jeff
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