Pyrefly Type Checking?

[rchen152]

Hi! I'm one of the maintainers of Pyrefly, which is a Python type checker and language server. We've recently migrated a couple projects in the pytorch ecosystem (pytorch/helion#1143, pytorch/pytorch#166197) to Pyrefly for faster type checking and better IDE support, and I was wondering if Ignite would be interested in migrating as well?

I've drafted a commit that would enable Pyrefly, so you can see what that would look like: rchen152@5233b91. Pyrefly does a full check in 1s, compared to 35s for Mypy. It does require more error suppressions for additional things it checks for, like possibly unbound variable names.

If this seems interesting, I can open a couple PRs (one to add Pyrefly, then a follow-up to remove Mypy and clean up some of the easy-to-fix suppressions).

[vfdev-5]

Hi @rchen152 , sounds interesting! When we first added mypy, it could reveal some flows in the code. I wonder whether ignored errors are real or limitations of purefly?
Yes, please go ahead with PRs to add purefly and then remove mypy and other as you proposed. Thanks!

[rchen152]

Awesome, I've opened #3474 to add Pyrefly.

I wonder whether ignored errors are real or limitations of purefly?

A lot of them are real errors, but there are also some pyrefly issues. For example, this line and this line look to me like legitimate errors. For the first one, the program will crash if ndims is any value except 2 or 3, since kernel_z will be undefined, and the second is due to an incorrect type annotation in Engine. But this one is due to a missing exhaustiveness check in Pyrefly.