from Hacker News

Pyrefly - A faster Python type checker written in Rust

by muglug on 4/29/25, 12:13 PM with 75 comments

  • by team_pyrefly on 4/29/25, 6:19 PM

    Hi Hackernews, I’m on the team working on Pyrefly at Meta. We address a lot of the comments in our FAQ: https://pyrefly.org/en/docs/pyrefly-faq/. I will try to address some questions directly too!

    Pyrefly is a work in progress, but you can install it from pypi and/or try our alpha VSCode extension if you are interested. You may still get false positive errors on your project as we are still burning down bugs and some features. We would love comments, bugs, or requests on our GitHub as you try it out.

    Lastly, one of our team members is giving a talk at PyCon about the design if folks are interested: https://us.pycon.org/2025/schedule/presentation/118/. We didn’t expect much attention before then, so thanks for taking a look!

  • by emptysea on 4/29/25, 3:17 PM

  • by nine_k on 4/29/25, 3:25 PM

    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.

  • by alexmolas on 4/29/25, 3:39 PM

    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.

  • by WD-42 on 4/29/25, 3:55 PM

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

  • by femtozer on 4/29/25, 3:08 PM

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

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

  • by odie5533 on 4/29/25, 10:44 PM

    This is awesome! Thank you for sharing it!

    I'm wondering though, why do existing tools like Mypy and Pyright not scale for Meta? Is Pyre(fly) being used extensively at Meta? In general what sort of issues did Meta run into?

  • by koakuma-chan on 4/29/25, 2:58 PM

    > 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.