Pyright was created to address gaps in existing Python type checkers like mypy.

Speed

Pyright is typically 5x or more faster than mypy and other type checkers that are written in Python. It is meant for large Python source bases. It can run in a “watch” mode and performs fast incremental updates when files are modified.

No Dependency on Python Environment

Pyright is written in TypeScript and runs within node. It does not require a Python environment or imported third-party packages to be installed. This is especially useful when used with the VS Code editor, which uses node as its extension runtime.

Configurability

Pyright supports flexible configuration that provides granular control over settings. Different “execution environments” can be specified for different subsets of a source base. Each environment can specify different PYTHONPATH settings, python language version, and platform target.

Type Checking Features

Pyright supports:

PEP 484 type hints including generics
PEP 526 syntax for variable annotations
PEP 544 structural subtyping
Type inference for function return values, instance variables, class variables, and globals
Smart type constraints that understand conditional code flow constructs like if/else statements

Built-in Type Stubs

Pyright includes a recent copy of the stdlib type stubs from Typeshed. It can be configured to use another (perhaps more recent or modified) copy of the Typeshed type stubs. Of course, it also works with custom type stub files that are part of your project.

Command-line or Language Service

Pyright includes both a command-line tool and a Language Server Protocol plugin for VS Code.

Language Service Features

Pyright offers the following language service features:

Hover tool tips that display type information
Links to symbol definitions
Smart priority queuing for “live” feedback during editing

Documentation

Limitations

Pyright currently provides support for Python 3.0 and newer. There is currently no plan to support older versions.

FAQ

Q: What is the difference between pyright and the Microsoft Python VS Code plugin?

A: The Python VS Code plugin is the official Python support extension for VS Code. It is officially supported by a team of engineers at Microsoft. It supports a diverse array of features including debugging, linter plugins, type checking plugins, and much more. Pyright is focused entirely on type checking. It is a side project with no dedicated team.

Q: What is the difference between pyright and the Microsoft Python Language Server?

A: The Microsoft Python Language Server is a language server protocol (LSP) implementation that works with the Microsoft Python VS Code plugin, and it is officially supported by a team of Microsoft engineers. It also provides type checking capabilities. Pyright provides overlapping functionality but includes some unique features such as more configurabilty, command-line execution, and better performance.

Installation

You can install the latest-published version of the Pyright VS Code extension directly from VS Code. Simply open the extensions panel and search for pyright.

The latest verison of the command-line tool can be installed with npm: npm i pyright

To install it globally: npm i -g pyright

To run the command-line tool: npx pyright <options>

Build Instructions

To build the project:

Install nodejs
Open terminal window in main directory of cloned source
Execute npm run install:all to install dependencies
Execute npm run build

To build the VS Code extension package: Same as above, plus

Execute npm run package

The resulting package (pyright-X.Y.Z.vsix) can be found in the client directory. To install in VS Code, go to the extensions panel and choose “Install from VSIX...” from the menu, then select the package.

Code Structure

client/src/extension.ts: Language Server Protocol (LSP) client entry point for VS Code extension.
client/typeshed-fallback/: Recent copy of Typeshed type stub files for Python stdlib
server/src/pyright.ts: Main entry point for command-line tool
server/src/server.ts: Main entry point for LSP server
server/src/analyzer: Modules that perform analysis passes over Python parse tree
server/src/common: Modules that are common to the parser and analyzer
server/src/parser: Modules that perform tokenization and parsing of Python source
server/src/tests: Tests for the parser and analyzer

TODO

Pyright is a work in progress. The following functionality is not yet finished. If you would like to contribute to any of these areas, contact the maintainers of the repo.

Add enforcement of covariance and contravariance
Type inference for generators and async functions
Support for old-style type annotations within comments
Address the many TODO comments in the code
Better handling of function decorators (don't punt on type checking)
Add lots of tests
Add support for type completion in VS Code extension
Special-casing @abstract methods so they don't need to return the specified type
Validate that all @abstractmethod are overridden
Validate parameters for magic functions
Validate that overridden methods in subclass have same signature as base class methods
Verify that exception classes inherit from base Exception
Validate await / async consistency
Flag assignments to read-only values (None, True, False, debug) as errors
Revamp support for properties - model with Descriptor protocol, detect missing setter
Add numeric codes to diagnostics and a configuration mechanism for disabling errors by code
Move error strings out of the main code files so they can be localized

Contributing

This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.

When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.