Talk Python To Me #523: Pyrefly: Fast, IDE-friendly typing for Python
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Oct 13, 2025 Danny Yang, a Meta engineer, joins Abby Mitchell and Kyle Into to explore Pyrefly, a groundbreaking, Rust-based type checker and IDE language server designed for fast Python typing. They discuss how Pyrefly significantly improves developer experience by reducing check times in massive codebases like Instagram from minutes to seconds. The team emphasizes Pyrefly's open-source nature, aiming to benefit the broader Python community. They also highlight how features like inference and type hints help both newcomers and experienced developers streamline their workflows.
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Pyrefly Is A Fast Dual-Purpose Tool
- Pyrefly is both a Python type checker and a language server written in Rust that emphasizes IDE features and speed.
- It infers many types even for unannotated code and serves as both CLI tool and fast editor integration.
Milliseconds Multiply Developer Productivity
- Millisecond-level speed improvements in IDE actions drastically improve developer productivity.
- Kyle reported a 90% speed increase for GoToDefinition on Instagram after switching to Pyrefly.
Instagram Drove The Need For Speed
- Danny explained Instagram's codebase scale and past tooling limits as context for Pyrefly's creation.
- Pyre took 15 minutes to check Instagram but Pyrefly reduced that to 15 seconds.
