Good stuff, quite right, and also introduces risk of one variable name shadowing another!

You missed one common case that's in flux these days, and that's class-level constants. When I first started coding Python, those too were ALL_CAPS but now most of the code I see has class level constants in snake_case. I believe it's the influence of things like SQLAlchemy.

It might be better if that weren't the case, but ALL_CAPS is a bit draggy to read, so I'm not going to complain about fashion.