"You can't just use functions defined in your tool, you need to create a faux-cli interface in order to run each parallel worker."

the multiprocessing library allows you to launch multiple processes using your function definitions. It's almost the same as the multithreading library but does not share data.

It seems the real problem, as you pointed out, is the additional memory. I didn't consider situations where each process would need an identical large data set, instead of just a small chunk to work on.