Using Python To Launch Python

[aha]

Hello All,
I have a situation where I can count on a Python installation being
available on a system, but I can't count on it being a version of
Python needed by my application. Since my application has it's own
version of Python installed with it how should I use the system Python
to launch the version of Python that launches my Application. Yes,
this is a convoluted process, but not all Pythons are built the
same

Right now I am leaning towards using exec to start a new process, but
I thought I would check to see if anyone else has had the need to
perform a task similar to this one.

AHA

 

[Derek Martin]

Since my application has it's own version of Python installed with
it how should I use the system Python to launch the version of
Python that launches my Application. Yes, this is a convoluted
process, but not all Pythons are built the same

/usr/local/bin/$APPNAME:

#!/bin/sh

INSTALLPATH=<wherever app is installed>
PATH=$INSTALLPATH/bin:$PATH
exec $INSTALLPATH/bin/python $APPNAME "$@"

Doesn't get much simpler than that. You can certainly do the
equivalent in Python... there's not much difference. Slightly less
typing in bourne/bash shell, I guess...

--
Derek D. Martin
http://www.pizzashack.org/
GPG Key ID: 0x81CFE75D


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[Mike Driscoll]

Hello All,
  I have a situation where I can count on a Python installation being
available on a system, but I can't count on it being a version of
Python needed by my application.  Since my application has it's own
version of Python installed with it how should I use the system Python
to launch the version of Python that launches my Application.  Yes,
this is a convoluted process, but not all Pythons are built the
same

Right now I am leaning towards using exec to start a new process, but
I thought I would check to see if anyone else has had the need to
perform a task similar to this one.

AHA

As an alternative, you may be able to use the subprocess module of
Python to do this too.

Mike

 

[Derek Martin]

You've hit the proverbial nail with the hammer. The problem is that my
application needs to run under both the Linux and Windows OSs, so while I
would love to use a nice sh, csh, or bash shell script. My hands are tied
because Windows does not provide such wonderful shells.

*Provides*, no... neither does it provide Python, for what that's
worth. But you can certainly get it (bash):

http://win-bash.sourceforge.net/

I suppose it's not worth installing just for this purpose though...
But you can provide with your application a DoS batch file that does
exactly the same thing (in addition to a shell script). The user
would quite intuitively use whichever were appropriate, or follow your
provided directions otherwise. Or, the equivalent in (hopefully
OS-agnostic) Python:

import os, sys

# I believe this gets the name of the root in all major OSes
def root_dir(path):
if os.path.dirname(path) == path:
return path
return (root_dir(os.path.dirname(path)))

appname = <name of your python script>
root = root_dir(os.getcwd())
install_path = os.path.join(root, "usr")
bin_path = os.path.join(install_path, "bin")
os.environ["PATH"] = bin_path + os.pathsep + os.environ["PATH"]
python_path = os.path.join(bin_path, "python")
args = sys.argv[1:]
args.insert(0, os.path.join(bin_path, appname))
args.insert(0, python_path)
args.insert(0, python_path)
os.execv(python_path, args)




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[Gabriel Genellina]

*Provides*, no... neither does it provide Python, for what that's
worth. But you can certainly get it (bash):

http://win-bash.sourceforge.net/

Using the standard cmd.exe, the previously posted shell script becomes:

=== begin appname.cmd ===
set INSTALLPATH=<wherever app is installed>
call %INSTALLPATH%\bin\python %INSTALLPATH%\APPNAME.py %*
=== end appname.cmd ===