Serious question, Do we need another type checker in Python?

I've never really felt the existing options were lacking for our use case. Completely fair game if this was just a passion project, but at this point at best this feels like noise, at worst some overzealous developer is going to implement this in my teams pipeline and waste time. Waste his time because the existing type checker did the job and there was not reason to change it, and waste our time because they will likely change (probably tighten) the existing behavior and waste our time while we adapt our habits to it.

The existing type checkers are slow. That's their reasoning for creating it. The type checking world in python is now reasonably well specified (and the type checkers are beginning to work more similarly), so I would expect (once ty is out of beta) you could replace your type checker with ty and just see a 20x speedup in CI and much much faster IDE diagnostics.

If it was going from 3s -> 1s then you'd probably be right, but on my work codebase pyright (which is the faster one!) takes 15 seconds (ty takes 0.8s) and takes a bit for errors to appear in the IDE. This is now fast enough for us (mypy was taking >30s, which was not fast enough), but if the project grew another order of magnitude (which it might) then it would probably be too slow.

It's the same reason ruff is great, linting the codebase is so so fast.