OSX-Launchd leaving processes open

I've written a script in Python that I call using launchd every night. The script uses a time delta to stop after a few hours. I'm finding that my plist file and script are working properly (launching and terminating at the appropriate times), but what I have come to see is that launchd is leaving a Python process open. This is causing almost a full core on my computer to be dedicated to a Python task. Is there an argument that I can pass to launchd to kill the Python task when my script has completed?