We’re building a new static type checker for Python, from scratch, in Rust.

From a technical perspective, it’s probably our most ambitious project yet. We’re about 800 PRs deep!

Like Ruff and uv, there will be a significant focus on performance.

The entire system is designed to be highly incremental so that it can eventually power a language server (e.g., only re-analyze affected files on code change).

Performance is just one of many goals, though.

For example: we're investing heavily in strong theoretical foundations and a consistent model of Python's typing semantics.

(We're lucky to have @carljm and @AlexWaygood on the team for many reasons, this is one of them.)

Another goal: minimizing false positives, especially on untyped code, to make it easier for projects to adopt a type checker and expand coverage gradually over time, without being swamped in bogus type errors from the start.

We haven't publicized it to-date, but all of this work has been happening in the open, in the Ruff repository.

All driven by a uniquely great team: @carljm, @AlexWaygood, @sharkdp86, @MichaReiser, @DhruvManilawala, @ibraheemdev, @dcreager.

I'm learning so much from them.

Warning: this project is not ready for real-world user testing, and certainly not for production use (yet). The core architecture is there, but we're still lacking support for some critical features.

Right now, I'd only recommend trying it out if you're looking to contribute.

For now, we're working towards an initial alpha release. When it's ready, I'll make sure you know :)

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[–] UFODivebomb@programming.dev 4 points 12 hours ago (2 children)

I don't think a powerful type system can be added to python effectively. Even more convinced of this after reading "minimize false positives".

Otoh, how strong of a type system is required for effective development? Probably what can be shoehorned into python tbh.

[–] FizzyOrange@programming.dev 3 points 5 hours ago

How powerful do you want it? Python's type system is actually pretty good already and relatively sound when checked with Pyright (not Mypy though).

It's not Typescript-level, but it's better than e.g. Java or C++.

The main problem is Python developers writing code that can't be statically type checked. E.g. using magically generate method names via __dict__ or whatever (I think lxml does that).

[–] vrighter@discuss.tchncs.de 1 points 11 hours ago

i don't believe it's possible either. For example the tree walker of the ast module takes the node passed to it, checks its type, gets its name, then looks for the method with that dynamically looked up name in your implementation of the tree walker and if it does (the user might not have implemented a visit method for that type of node), calls it and passes the node to it. All of this at runtime.