Here are a couple of online resources and downloadable items.
This was the first designspace package in Python. Largely superseded by FontTools varlib. But it has some perks that makes it remarkably useful. MutatorMath on Github
UFOProcessor slices and dices and generates instances. If you want to integrate designspace stuff into your Python workflow, this can be useful package. UFOProcessor on Github
Lightweight font objects built for speed and math: FontMath on GitHub
Batch is a RoboFont extension to generate binary fonts in batch. It can also generate instances from designspaces. Batch on Github
A PDF with some suggestions on how to construct letterforms with overlapping shapes.