Creating a subprocess in python

Question

I am trying to use th subprocess module along with the Popen class to create and run a process. Up until now, I always succeeded calling any program I wanted.

Now I am trying to call paraview (version 3.8.1) with a python script attached to it as a parameter like so:

paraview --script=script.py

If I run this command from console it works just fine. If I try to run it with my Popen class it fails with the error message:

/home/woltan/local/lib/python2.7/site.py:157: Warning: 'with' will become a reserved keyword in Python 2.6
'import site' failed; use -v for traceback
/home/woltan/local/lib/python2.7/linecache.py:127: Warning: 'with' will become a reserved keyword in Python 2.6
/home/woltan/local/lib/python2.7/site.py:157: Warning: 'with' will become a reserved keyword in Python 2.6
'import site' failed; use -v for traceback
ERROR: In /home/kitware/Kitware/ParaView-3.8.1/source/Utilities/VTKPythonWrapping/Executable/vtkPVPythonInteractiveInterpretor.cxx, line 75
vtkPVPythonInteractiveInterpretor (0x124e9d0): Failed to locate the InteractiveConsole object.

Paraview itself is starting up. But is the error message due to the fact, that paraview itself has a python interpreter which it is using? Or can I tweak my Popen calling routine which looks like this:

p = subprocess.Popen("paraview --script=script.py", bufsize = -1, shell = True)

How can it be, that a process can be created from console but not with the Popen-call from above?

Edit

I downloaded and installed a paraview version where python 2.7 is running inside (and not python 2.5 of the version I used above) and the call of Popen works. So this must have something to do with the python version of paraview. The only question remaining is: Why does it even matter when I start a process with Popen?

Answer 1

There are 2 things which are strage:

1. Normally, this call shouldn't work at all. As you have shell=False, you would need to use a sequence as 1st parameter:

   p = subprocess.Popen(("paraview", "--script=script.py"), bufsize=-1)
   

   (shell=False is the default.)

2. You seem to mix several Python versions:

   /home/woltan/local/lib/python2.7/site.py:157: Warning: 'with' will become a reserved keyword in Python 2.6
   

The said site.py uses the with keyword. That's ok, because it is intended for Python 2.7. The python version you are running seems to come from Python 2.5. There was no with back in 2.4, and in 2.6 it was already present.

Answer 2

The error message you're getting doesn't seem to be related to subprocess.Popen. I'd say that what you need is either shell=True:

p = subprocess.Popen("paraview --script=script.py", shell = True)

or separate args in a sequence:

p = subprocess.Popen(['paraview', '--script=script.py'])

I've never used bufsize, but I don't think it makes any difference here.