Starting jython program from python using subprocess module?

Question

I have a jython server script (called rajant_server.py) that interacts with a java api file to communicate over special network radios. I have a python program which acts as a client (and does several other things as well). Currently, I have to start the server first by opening a command/terminal window and typing:

cd [path to directory containing rajant_server.py
jython rajant_server.py

Once the server successfully connects it waits for the client, which I start by running:

cd [path to directory containing python client program]
python main.py

When the client connects, the server prints out information (currently for debug) in it's command/terminal window, and the client program prints out debug information in it's command/terminal window. What I want to do is do away with the complex process by calling jython from my 'main.py' program using the subprocess module.

The problem is two fold:

1 - I need the rajant_server.py program to open in it's own terminal/command window

2 - jython needs to be run in the directory where the rajant_server.py file is stored, in other words, typing the following into the command/Terminal Window doesn't work (don't ask me why):

jython C:/code_dir/comm/server/rajant_server.py

but:

cd C:/code_dir/comm/server
jython rajant_server.py

does work.

Okay... I just got something to work. It seems like a bit of a hack, so I would still love ideas on a better approach. Here is what I am currently doing:

serverfile = r'rajant_server_v2.py'
serverpath = os.path.join(os.path.realpath('.'),'Comm',serverfile)
serverpath = os.path.normpath(serverpath)
[path,file] = os.path.split(serverpath)

command = '/C jython '+file+'\n'
savedir = os.getcwd()
os.chdir(path)
rajantserver = subprocess.Popen(["cmd",command],\
        creationflags = subprocess.CREATE_NEW_CONSOLE)

#Change Directory back
os.chdir(savedir)
#Start Client
rajant = rajant_comm.rajant_comm()
rajant.start()

If you have a solution that will work in both linux & windows you would be my hero. For some reason I couldn't change the stdin or stdout specifications on the subprocess when I added creationflags = subprocess.CREATE_NEW_CONSOLE.

If anyone can find an elegant way to have popen work on both Windows and Linux, I will create a bounty and award rep. — Rafe Kettler
– Rafe Kettler, Commented Nov 9, 2010 at 2:49
Why not create simple .bat/bash script that starts both programs? — Michał Niklas
– Michał Niklas, Commented Nov 9, 2010 at 9:19

spacedentist · Accepted Answer · 2010-11-11 15:40:08Z

1

The Popen function in subprocess accepts an optional parameter 'cwd', to define the current working directory of the child process.

rajantserver = subprocess.Popen(["cmd",command],\
        creationflags = subprocess.CREATE_NEW_CONSOLE,\
        cwd = path)

You can get rid of the os.getcwd call and the two os.chdir calls this way. If you want to be able to use this script on Linux, you have to do without 'cmd'. So call Popen with ["jython", file] as first argument.

EDIT: I've just seen that CREATE_NEW_CONSOLE is not defined in the subprocess module when running on Linux. Use this:

creationflags = getattr(subprocess,"CREATE_NEW_CONSOLE",0),\

This will be the same as before, except it falls back to the default value 0 when the subprocess module does not define CREATE_NEW_CONSOLE.

answered Nov 11, 2010 at 15:40

spacedentist

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