How to call an external program in python and retrieve the output and return code?

Look at the subprocess module: a simple example follows...

from subprocess import Popen, PIPE

process = Popen(["ls", "-la", "."], stdout=PIPE)
(output, err) = process.communicate()
exit_code = process.wait()

Check out the subprocess module here: http://docs.python.org/library/subprocess.html#module-subprocess. It should get what you need done.