Pyrefly

Pyrefly is one of the major new Python type-checkers taking the world by storm. It's often touted for its speed, usability, and typing-spec-conformance. But it also offers an extra nifty little feature you may never have heard of: type-coverage. Let's lea

Pyrefly v1.2 is now available This release adds support for Bazel and attrs, along with improvements to type checking, the language server, and the CLI. This release includes 901 commits from 59 contributors. To get started, run: pip install --upgrade pyr

Companion post to my PyCon 2026 Typing Summit talk, "From Soundness to Blame: AI-Assisted Formalization of a Tiny Python." This is the first in a series. What this series is about Python's type system is practical, useful, but full of edge cases. As a dev

Built-in support for attrs is available in Pyrefly as of version 1.2.0-dev.1, and ships in the upcoming 1.2.0 stable release. You get accurate constructor signatures and better type safety for your attrs classes, with no plugins or configuration to set up

Pyrefly v1.1 is now available This is our first minor release since reaching stable v1.0 in May, and it brings improvements across the board: better performance, smarter type checking, and new IDE refactoring tools. This release bundles over 250 commits f

Why aren't tensor shapes part of the type system? When you write a PyTorch model, the hardest part of composing tensor ops is keeping track of their shapes. The standard practice today is to write shapes down as comments as you go. This talk introduces an

Does adding type checking to an agentic workflow really help agents? We ran an experiment recently to determine whether there are improvements in the success rate for completing different kinds of tasks. In theory, having a type checker present should hel

Meta's Rust-powered linter and type checker for Python pairs blazing speed with advanced and innovative features.

Mypy, Pyrefly, Pyright, ty, Zuban, and possibly more that will come in the future... how are library maintainers expected to cope? TL;DR: Prioritise running as many type-checkers as possible on your test suite. Run at least one on your source code. The ty