I've forgotten by this point, but I think the reason I rewrote the whole tool in Ruby the other day was that I wanted to be able to use a specific Ruby epub library I'd found. Python has nothing anywhere near as usable. Anyway, wasn't a hard project. Half of an afternoon to get it going, and most of that time was spent generalizing (aka dehackifying) parts of my infrastructure.
Yeah. I'm procrastinating. You figured it out.