100k lines of Python? I find it hard to believe that this project is properly organized. Rarely do you see 100k lines of Python solving a single problem, instead a project will be divided into many components, some of which can be reused in other projects. There shouldn't be any difference working on 1k line or 1 million-line code bases as long as the code is decoupled. Testing each part in isolation helps a lot (as opposed to running tests for a big monolithic ball of mud), as it ensures contributors are not introducing crazy dependencies.
I'm not against types at all, but don't think they solve problems related to big code bases.
Is there ever a project of that size that's properly organized? We did our best under the constraints we had. There was always a long wishlist of things we would change if we had the time, and some of them we were able to do.
I'm not against types at all, but don't think they solve problems related to big code bases.