As another commenter said, renaming the symbol “ureg” to “units” would improve readability. I am not sure if I would ever use this (the code for unit conversion in my ancient, not touched in a decade, recipe site cookingspace.com for conversions was very simple). However, I spent ten minutes looking at the source code and realized I should improve my Python-Fu. I use Python a lot for deep learning and NLP work but I seldom use Python in the way I use Lisp languages. I might enjoy Python more if I took a deeper dive.

Anyway, cool project.