Comment by kingkongjaffa | Hacker News Reader

Comment by kingkongjaffa | Hacker News Reader

This is very cool but why wouldn’t they just contribute to uv and ruff and ty https://github.com/astral-sh/ty

I think astral and meta were both working on their own type-checkers independently. My current understanding is that meta released so they could preempt the initial release of ty. It seems like they're a bit further ahead in development. Not sure if there are going to be any real differences between the two down the line.

Sounds a lot like TypeScript and Flow.

Typescript was Microsoft though. Meta might have the edge here based on brand awareness, but who knows for sure.

Right, and Flow was FB

Sure, but in this case they are both implementations of a spec defined by PEPs, so a bit more like gcc vs clang (less tightly bound than those, of course, in design decisions). Neither company is trying to invent a new language here.

The current major type checkers, mypy and pyright, are also based on the same PEPs, but you can still see differences between them. For example, my codebase passes pyright in strict mode, but mypy results in a bunch of type errors. I'd expect pyrefly and ty to be slightly different from each other.

See also:

https://github.com/microsoft/pyright/blob/main/docs/mypy-com...

https://htmlpreview.github.io/?https://github.com/python/typ...

Sure, I agree. I’m just saying that most of their defacto disagreements are because of ambiguity in the specs, not because one of them is (intentionally) choosing to fork.

Fwiw I think performance and features are kind of intertwined here, since Pyright’s extra speed makes it possible to infer more things that are not easy for mypy, especially in an LSP implementation.

Pyright is very impressive in that second link (conformance check), very much a product of Eric Traut & others dedicating a lot of energy to this single problem.

the specs are still evolving, and the various type checker implementations are what is driving them forward. in general, capturing the dynamic typing semantics of python in a gradually typed system is not a fully solved problem, and the type checkers are experimenting with various approaches to it.

I think they've mentioned earlier that it's really just because PyCon is this week (so a good time to announce new Python tooling).

That's sort of how I felt about things before, but the reality I believe is we wouldn't have uv if they 'just contributed to poetry'.

I tend to agree.

I don't know the differences between the two well enough to know if it was the case here, but in my experience sometimes you need to innovate on a fork, or from scratch in order to create the space/freedom to do so.

Once a project is popular, it's harder to justify and be confident about major changes (aka https://m.xkcd.com/1172/)

It seems like the share a lot of the same goals but my impression is Poetry is much slower to pick up on standards. It’s normal to use uv with a project now that doesn’t have any [tool.uv] section in pyproject.toml at all but every poetry project I’ve seen is littered with [poetry] sections, even dependencies. Makes me not want to use it

ty is so new right now - it only got its current name a few weeks ago!

That’s not true, they have been developing it as red knot for a good while :)

Like I said, it only got its name a few weeks ago.

I just ran ty and it can't resolve any imports whereas pyrefly passes. Why would that be? I hate Python so much.

ty doesn't invoke a Python interpreter to discover imports yet — so you need to either set `VIRTUAL_ENV` or pass `--python` to configure your target environment. We'll expand support here in the future, but this part of ty's interface is intentionally minimal while we focus on core type checking features.

> I hate Python so much.

Look I get that it's frustrating, but the tool you're whinging about is literally pre-alpha.

I love the language, but I do hate the import system too, it makes everything harder

I just put __init__.py everywhere, not sure it does something but to be safe

NIH + copyright

Isn't both this and ty MIT license?

Because this has been tested at Meta / Facebook scale which means it's faster for any Python codebase massive and small.

Since Meta built this, I have confidence this will be maintained more than others and I will use this and ask for Pyrefly experience in the future.

I suggest you try uv and ruff and then see if you still think only companies the size of meta can provide quality tooling.

This feels like a somewhat closed minded approach given both tools are in their infancy

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