It's not my project; I'm just a collaborator. My experience has been that a very tiny minority of Python code out there is written in this style, so unless you're only starting projects from scratch, you can't benefit from it.

you can gradually type (probably don't use --strict in that case). It might not be a ton of benefit if you aren't actually writing new code though.

There's a good document on this:

https://mypy.readthedocs.io/en/latest/existing_code.html

And that'd be fine if everyone were on board with it and that were the general direction of the project, but I don't think that's true.

I've never seen a strict, type-annotated Python project out there in the wild, and I've seen a decent amount of them. A random non-primary-contributor isn't going to have much luck stepping into an established project and getting everyone to go along with adding annotations to the whole thing.

And if I were starting a project from scratch, rather than coercing the language to do something it wasn't really designed for, I'd just use a language that has first-class support for types directly in the compiler, like Java or Go.

But at that point why not get something for they time you spend adding types and just use a different language?