Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Pyrefly: Python type checker and language server in Rust

pyrefly.org

Post reply on HN
Print view View original

41–50 of 150 posts

Re: Pyrefly: Python type checker and language server in Rust

#41

Post by Scarblac »

giancarlostoro wrote: post #29
pawelkobojek wrote: post #11

I love the speed advantage of pyrefly over (based)pyright but so far it doesn't seem to highlight as much as pyright does, for example it doesn't catch unreachable code like this: def fn(x: str): if x is None: x = "123" # pyright flags that as unreachable code, pyrefly does not Autocomplete for modules also doesn't work for me yet: import os os. # I'll get `ABC, `Any`, `AnyStr`, `AnyStr_co`, `BinaryIO`, ... Looking f…

It's funny because in other typed languages a string can be null because of string being a reference type as opposed to a value type. I think Python type hints make more sense than C# does in this respect, which gives me a chuckle (two of my favorite languages and the untyped one makes more sense with types). That said, not sure if you already have but I would add a github issue / ticket reporting your issue to raise…

All Python types are reference types. The reference to None isn't included in the str type.

There's no way to get an actual null reference, afaik. Variables always have some value, possibly None.

(not sure what happens if you set a reference to null from C - a crash, probably?)

Re: Pyrefly: Python type checker and language server in Rust

#42

Post by codethief »

rasulkireev wrote: post #32

This looks interesting. But I decided to go with ty in my projects, for the incremental approach.

How well does ty work these days? Last time I checked it still produced a lot of false positives and false negatives. (Which was very much expected, given its alpha/WIP status.)

Re: Pyrefly: Python type checker and language server in Rust

#43

Post by [deleted] »

sirfz wrote: post #38

I've decided to to try out Pyrefly, Ty and Zuban for their language server features (type checking disabled where possible) last week and found that Zuban is the fastest (but unfortunately doesn't currently have the option to disable type checking). Ty comes next and Pyrefly was surprisingly slow to load (have to wait a few seconds before I can goto definition for example). They all lack certain features vs basedpyri…

[deleted]

Re: Pyrefly: Python type checker and language server in Rust

#44

Post by pjmlp »

whalesalad wrote: post #15

Python is starting to feel a bit like JavaScript circa 2014. Remember grunt, gulp, webpack, coffeescript, babel? Now we've got pyright, mypy, pyrefly, black, ruff, ty, flake8, poetry, uv... I used to find this kind of tooling explosion exhausting (and back then with JS it truly was), but generally speaking it's a good sign that the community is hungry to push things forward. Choice is good, as long as we keep the Uni…

Pity that is all looking like Rewrite in Rust looking for solution, instead of actually improving JIT tooling capabilities.

There is a reason us old timers mostly wait on the sidelines until the dust settles.

We have seen this movie already too many times.

Re: Pyrefly: Python type checker and language server in Rust

#45

Post by phailhaus »

flanked-evergl wrote: post #37

Sadly, the question with both this and ty is: Does it support pydantic? If not, then it's not really helpful for many people, and right now AFAIK neither supports pydantic. Pydantic is probably the problem here, but it is what it is.

Python's type system is the problem here, which cannot support even the native dataclass pattern and needs custom plugins written for each type checker.

Re: Pyrefly: Python type checker and language server in Rust

#47

Post by jswny »

sirfz wrote: post #38

I've decided to to try out Pyrefly, Ty and Zuban for their language server features (type checking disabled where possible) last week and found that Zuban is the fastest (but unfortunately doesn't currently have the option to disable type checking). Ty comes next and Pyrefly was surprisingly slow to load (have to wait a few seconds before I can goto definition for example). They all lack certain features vs basedpyri…

At least for Ty, not sure about the others, it is explicitly for type checking, exposed as an LSP. It’s not trying to compete with full LSP implementations. Most modern editors let you combine multiple LSPs, you shouldn’t think of them as using only one at a time

Re: Pyrefly: Python type checker and language server in Rust

#48

Post by asplake »

_flux wrote: post #36
giancarlostoro wrote: post #29

Earlier quoted context omitted.

It's funny because in other typed languages a string can be null because of string being a reference type as opposed to a value type. I think Python type hints make more sense than C# does in this respect, which gives me a chuckle (two of my favorite languages and the untyped one makes more sense with types). That said, not sure if you already have but I would add a github issue / ticket reporting your issue to raise…

In some other typed languages, that is. E.g. in C++, OCaml, Haskell, F#, Kotlin, and Rust (a non-exhaustive list) you can have non-nullable strings, and other objects.

It’s worth noting that even though the runtime allows nulls (i.e. None) anywhere, Python type checkers do distinguish between optional and mandatory types.

Re: Pyrefly: Python type checker and language server in Rust

#49

Post by cruffle_duffle »

jon-wood wrote: post #34
jerrygenser wrote: post #4

Earlier quoted context omitted.

Basedpyright is not rust but it's a fork of pyright with added features that are otherwise locked in vscode

I'm sorry, I can't take seriously any piece of software which decided to prefix the previous version's name with "based". I'm aware this is a me problem.

Hah. I love the name. It implies that whatever the original “pyright” was doing wasn’t keepin’ it real. This new version, it’s “based” so it must be somehow more “real” and “grounded” and “legit”.

All I know is it is much more strict about stuff than pylance was.

Also a me problem!

Re: Pyrefly: Python type checker and language server in Rust

#50

Post by scosman »

emddudley wrote: post #10
scosman wrote: post #9

Anyone know how this compares to 'ty': a new typechecker from Astral (uv/ruff team), also written in Rust and super fast. I had been waiting on it to reach beta, but would love to move to something faster than pyright sooner if possible.

Pyrefly vs. ty: Comparing Python’s Two New Rust-Based Type Checkers (2025-05-27) https://blog.edward-li.com/tech/comparing-pyrefly-vs-ty/ HN discussion of above: https://news.ycombinator.com/item?id=44107655 How Well Do New Python Type Checkers Conform? A Deep Dive into Ty, Pyrefly, and Zuban (2025-08-29) https://sinon.github.io/future-python-type-checkers/

amazing reply. Thanks!
Post reply on HN