My iMac's automated backup has been broken since Yosemite because Apple removed the ability to set environment variables that all processes started from launchd could use.

It appears that "run a python program as root on a schedule regardless of if anyone is logged in" is no longer possible on a Mac. Or rather, me and my CS PhD aren't capable of figuring out how to do it. I just keep a terminal window open at all times as a reminder to occasionally manually run the script.