Pyrefly - A faster Python type checker written in Rust

https://pyrefly.org/

94•muglug•6h ago

Comments

koakuma-chan•3h ago

> pyrefly check --suppress-errors

> INFO 5,240 errors shown, 65,932 errors ignored

Not a single Python type checker had ever worked for me so far.

kstrauser•3h ago

I don't see the link between that output and your conclusion. Are those results wrong?

koakuma-chan•3h ago

> Are those results wrong?

I don't know. Some packages just don't work with type checkers, e.g. Django.

masklinn•2h ago

Django has a community stubs project, are you using it?

johnisgood•2h ago

Is it not that he used the "--suppress-errors" flag yet it did not ignore the errors?

kstrauser•1h ago

It's hard to tell. Other similar options in other commands can mean things like "exit with status 0 even if errors are detected". Without installing pyrefly, I'm not sure what that flag's supposed to do. It's not documented on their site.

koakuma-chan•1h ago

It adds a comment to suppress the error above each line in your codebase that causes an error, but it reports the errors before doing that, so you can only see the result after you re-run `pyrefly check`.

kstrauser•1h ago

Oh! That's nifty. It leaves you with a baseline so you can stop making new mistakes, and gives you something to grep for when you want to fix existing ones.

ipsum2•3h ago

It's literally working? What did you expect?

koakuma-chan•3h ago

Maybe it's working but it's not useful.

masklinn•2h ago

What would you expect "useful" to be if your codebase is basically incompatible with type checking?

koakuma-chan•2h ago

I expected that I would be able to run the check command and it would just work. Upon reading the docs, this tool recommends incremental adoption, and after using `--suppress-errors`, `# pyrefly: ignore` is all over my codebase.

Yossarrian22•2h ago

…how else would it work?

nerdponx•2h ago

That's incremental adoption for adding type hints, not for adopting this particular tool in an already-type-hinted codebase.

krick•2h ago

I know I shouldn't get into this thread, but I'm extremely curious: what did you expect should have happened? I mean, literally, what do you mean by "just work", what work did you expect a type checker to perform if not to show you errors?

koakuma-chan•2h ago

I expected a reasonable amount of reasonable errors, not 60k+ errors most of which are import-error, even though the code runs fine.

edit: most errors weren't actually import-error, I just misunderstood --search-path

ForHackernews•3h ago

Fix your types.

IshKebab•2h ago

Do you... have type annotations? I think you might be missing the point.

jon-wood•2h ago

I think the point here is that for something like Python the default behaviour should be an assumed return type of `Any` rather than throwing an error. Maybe that is the case and the GP had configured it otherwise.

femtozer•3h ago

The team behind ruff/uv is working on a similar tool:

https://x.com/charliermarsh/status/1884651482009477368

joshdavham•2h ago

Have there been any updates on when they think it’ll be released?

singhrac•2h ago

At least the alpha milestone is May 12, but I don't think they've publically committed to anything.

In particular for me it would be great to have a better typechecker than Pyright available for Zed (basically why the editor is a nonstarter right now).

Y_Y•2h ago

An editor is a nonstarter because it doesn't doesn't integrate the right implementation of some particular optional feature for some particular language?

That's a high bar!

drcongo•1h ago

I have some sympathies with the parent post as Zed is my daily driver and I mostly write Python. Pyright is horrible to work with, tons of false positives. Parent poster - you might find this useful: https://github.com/zed-industries/zed/discussions/24801

hopfenspergerj•1h ago

No it is not horrible to work with. Even the “standard” settings are quite lax.

WD-42•1h ago

So what editor is a starter then? As far as I know pyright is the de facto checker for python in most editors. Not sure why it would be worse in zed, seems to work fine for me. Or as well as pyright can work.

emptysea•2h ago

A rewrite of https://github.com/facebook/pyre-check in rust?

codethief•1h ago

My thought exactly! Maybe for performance reasons? (Though I wouldn't expect OCaml to perform that badly, either…)

nine_k•2h ago

On one hand, "launching Spring 2025". On the other hand, 47% complete, with a ton of basic stuff not yet ready. I wonder how fast they plan to move, given that only 32 days remain of the spring.

Vinz_•2h ago

We’re 53 days away from summer though.

rplnt•2h ago

Not in southern hemisphere.

croemer•1h ago

It's not "47% complete", it's just that (now) 52% of the issues in a milestone are complete.

alexmolas•2h ago

The astral team (behind uv and ruff) is already working on a type checker in Rust, and given the quality of their existing tools, I'm inclined to wait and see what they release. Pyrefly looks interesting, but from the repo it seems pretty early-stage and not intended for external use yet.

maxloh•2h ago

It is codenamed "Red Knot".

Refer to the crates starting with red_knot in this directory to follow its development: https://github.com/astral-sh/ruff/tree/main/crates

The latest commit was only an hour ago.

nemith•1h ago

Also Facebook has a history of releasing the source code for something. Making a huge splash and then essentially doing nothing after 3 months (aka after someone gets their review).

They use the code internally but fail at making sure it has use externally. This is doubly the case for anything infrastructure

Buck2: Was released. Never could be built correctly without the latest nightly of Rust and even then it was fragile outside of Meta's build architecture

Sapling: Has a whole bunch of excitement and backing when it was announced. Has been essentially dead 3 mos after release.

I used to work for Meta infra. I know the MO. Have a hard time trusting.

Astral use-case is external and has a better chance of actually being supported.

wocram•1h ago

Is this standard promotion driven development? Or do the people who are trying to open source these products end up being blocked?

ipsum2•1h ago

Sapling is actively developed, not "dead after 3 months": https://github.com/facebook/sapling/commits/main/

Have not tried building Buck2 (no personal use for it), but its also actively developed: https://github.com/facebook/buck2/commits/main/

jihadjihad•1h ago

At first I thought this was the release from Astral for their type checker. Same boat, sitting tight, holding champagne ready for that day too.

WD-42•2h ago

Cannot wait to get rid of pyright, but I’ll be holding out for Astrals type checker.

nikisweeting•2h ago

I've loved pyright so far, what do you dislike about it?

ndr•1h ago

It's slow as hell. And every version bump comes with a bunch of new warnings/errors by default that is quite disruptive if you want to keep it quiet. But mostly that it is annoyingly slow.

emptysea•1h ago

Might be worth checking out https://github.com/DetachHead/basedpyright

But I’ve had the same issue with too many warnings, mypy is better at understanding Python but even slower.

addoo•1h ago

I guess it’s all relative. One of my code bases still has pylint running with only a couple custom lint rules, that one is slow as hell.

As for version bumping, maybe it’s just a me thing, but I hard fix a version and only update occasionally. Sure each update brings new warnings, but most of them are valid and if you only do it a couple times a year… not that big a deal.

WD-42•1h ago

Try ruff instead of pylint. It will open your eyes to how performant software can actually be. All of us that have been working in python and JavaScript for too long have really forgotten.

addoo•1h ago

We use ruff for everything that isn’t a custom rule.

The only thing I found it ‘missing’ was an indentation check (it’s in preview, I don’t turn on preview rules), but I realized it doesn’t matter because we also have a formatter running on everything.

WD-42•1h ago

It’s dog slow. I realize we are talking about a python checker written in typescript, so two relatively slow languages combined, but still.

The dependency on node makes it a PITA to set up in non-vs code environments as well.

insane_dreamer•7m ago

pyright doesn't do well with inspecting inherited types, at least in our experience. Falls far behind JetBrain's type checker in Pycharm. (This is one reason why pycharm >> zed.)

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Pyrefly - A faster Python type checker written in Rust

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