Pyrefly: Python type checker and language server in Rust

Post by notatallshaw » Tue, Oct 14, 2025, 3:56 PM UTC

eqvinox wrote: post #76

notatallshaw wrote: post #71

Earlier quoted context omitted.

> Hmm. Presumably mypy and pyrefly use the same ones, but then I don't understand why pyrefly is complaining and mypy isn't: > …where is it even puling "tuple[Any]" from… Perhaps it's a bug in pyrefly, perhaps mypy or pyrefly is able to infer something about the types that the other isn't. I would strongly suggest checking their issues page, and if not seeing a report already report it yourself. While there is an ong…

> it does not actually cover what rules you can check or infer from type hints Indeed this is the cause of maybe 30% of the warnings I'm seeing… items being added to lists or dicts in some place (or something else making it infer a container type), and pyrefly then refusing other types getting added elsewhere. The most "egregious" one I saw was: def something(x: list[str]) -> str: foo = [] for i in x: foo.append(i) r…

    foo: list[str] = []

  * What can I infer from an empty collection declaration?
  * What do I allow further down the code to update inferences further up the code?

Post by koakuma-chan » Tue, Oct 14, 2025, 3:59 PM UTC

parhamn wrote: post #23

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…

Interestingly besides typescript, javascript in 2025 is still super fragmeneted but by a bunch of well-polished tools that all do approximately the same thing. esbuild/vite(rollup)/trubopack(swc), prettier/biome/oxc, npm/bun/pnpm/yarn, bun/node/deno/worker-runtimes

Post by pjmlp » Tue, Oct 14, 2025, 4:11 PM UTC

parhamn wrote: post #23

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…

Interestingly besides typescript, javascript in 2025 is still super fragmeneted but by a bunch of well-polished tools that all do approximately the same thing. esbuild/vite(rollup)/trubopack(swc), prettier/biome/oxc, npm/bun/pnpm/yarn, bun/node/deno/worker-runtimes

Post by lenkite » Tue, Oct 14, 2025, 4:14 PM UTC

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…

Post by coldtea » Tue, Oct 14, 2025, 4:33 PM UTC

phplovesong wrote: post #67

screye wrote: post #66

Earlier quoted context omitted.

If ruff & uv have proved anything, it's that a tool that's effortless, a net-positive and fast will get adopted. New typecheckers don't need to be perfect. They need to be good enough, easy to integrate and have low false positives. Sure, they will improve with time, but if feels like a pain then no one will pick it up. Python users are famously averse to tools that slow down their dev cycles, even if it means better…

If typechecking is tongue on cheek, why even bother?