Spawning a new UI process

[Ed Leafe]

I'm working on a wxPython app (well, a Dabo app, but it's basically
the same thing) that presents the user with a selection of several
wxPython apps that exist on their system. They choose one, and I want
to then "launch" that app, as if they had typed "python myapp.py" from
a terminal window. The initial app can either terminate or continue;
that's not terribly important. The important thing is to get the
selected app to run in a separate process.

I've tried all the variants of os.spawn* and os.exec*, without
success. Either nothing happens, or a Python interpreter is opened in
the Terminal window I used to run the launcher. I want to do something
like:

cd (appdir)
pth = os.path.join(os.getcwd(), "main.py")

followed by one of:

os.spawnl(os.P_NOWAIT, "main.py")
os.spawnl(os.P_NOWAIT, pth)
os.spawnl(os.P_NOWAIT, "python", pth)
os.spawnl(os.P_NOWAIT, "python", "main.py")
os.spawnl(os.P_NOWAIT, "/usr/bin/python", pth)
os.spawnl(os.P_NOWAIT, "/usr/bin/python", "main.py")

The only result I've gotten is a Python interpreter is started, but
the GUI app that should be launched by 'main.py' is never run.

So what am I missing? How do I launch a python app in a separate
process from another Python app?
-- Ed Leafe