Pyrefly is a Python type checker and language server developed by Meta. Written in Rust, it is designed to improve development productivity by identifying type inconsistencies and providing useful information about source code while developers are working.
The application combines static type analysis with an understanding of program control flow. It can infer information about variables and return values, helping developers identify potential errors without requiring every expression to be explicitly annotated.
Pyrefly is suitable for individual projects and larger codebases where checking performance can become an obstacle to adopting stronger typing practices. Its command-line and editor interfaces share the same underlying analysis capabilities, allowing the tool to be incorporated into interactive development and automated checking workflows.
This is free and open source software.
Key Features
- Supports incremental checking and parallel processing to reduce analysis times when working with large projects.
- Infers variable and return types, reducing the need for unnecessary explicit annotations.
- Uses control-flow analysis to narrow types within conditional statements and other program structures.
- Provides language server functionality, including completion, navigation, hover information and semantic highlighting.
- Offers inlay hints and other editor assistance for understanding inferred types.
- Supports advanced typing constructs and selected framework-specific patterns.
- Provides configuration options for controlling diagnostics and project analysis.
- Can be incorporated into existing development workflows through its command-line checker and compatible editors.
Website: github.com/facebook/pyrefly
Support:
Developer: Meta Platforms, Inc. and affiliates
License: MIT License
Pyrefly is written in Rust. Learn Rust with our recommended free books and free tutorials.
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Read our verdict in the software roundup.
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