I’ve tried to get mypy into our main Django app, and the project suffers greatly from library annotations.
Typescript has a project (Typeshed) that includes type annotations for JS libraries. Mypy has one too.
Unfortunately, Mypy’s Typeshed requires approval from the third party libs to check in any library stubs. Plus there’s a “notability requirement”. This means that while I can find annotations for many minor projects in typescript, Mypy has basically nothing. So if you try to use this with “production code” (including third-party things), then you’re out of luck.
This is unbelievably frustrating because Typescript has almost single-handedly (along with moving to Angular) saved the sanity of my team. We’re all proud Pythonistas, but the policies that MSFT(?, not sure if they were managing Typeshed before) took for dealing with 3rd party stuff was super successful.
EDIT: I’m complaining but we’re actively looking for ways around this. Mypy has an automated stub generator but it’s half broken. Maybe we’ve overestimated the readiness of this tool (despite it being talked about a lot recently)