# Pyright — Fast Static Type Checker for Python

> Pyright is a high-performance Python type checker written in TypeScript that provides real-time type analysis, type inference, and IDE integration.

## Install

Save as a script file and run:

# Pyright — Fast Static Type Checker for Python

## Quick Use
```bash
pip install pyright
pyright src/
```

## Introduction
Pyright is a static type checker for Python created by Microsoft. Written in TypeScript and running on Node.js, it delivers significantly faster analysis than traditional Python-based type checkers, making it practical for large codebases with millions of lines.

## What Pyright Does
- Performs full static type analysis of Python code using PEP 484 type annotations
- Infers types for unannotated code using flow-sensitive narrowing and control flow analysis
- Reports type errors, missing imports, and unreachable code at development time
- Powers the Pylance VS Code extension for real-time editor diagnostics
- Supports all typing constructs including generics, protocols, TypedDict, and ParamSpec

## Architecture Overview
Pyright parses Python source files into an AST, then runs multiple analysis passes: import resolution, scope analysis, type evaluation, and type narrowing. Its incremental architecture re-analyzes only changed files and their dependents. Because it runs on Node.js rather than CPython, startup and throughput are substantially faster than mypy for equivalent codebases.

## Self-Hosting & Configuration
- Install via pip (`pip install pyright`) or npm (`npm install pyright`)
- Configure through a `pyrightconfig.json` file at the project root
- Set `typeCheckingMode` to basic, standard, or strict for varying rigor levels
- Define `include` and `exclude` paths to control which files are analyzed
- Use `venvPath` and `venv` settings to point Pyright at virtual environments

## Key Features
- Analyzes large codebases 3-5x faster than mypy due to TypeScript runtime
- Watch mode re-checks only affected files on save for near-instant feedback
- Supports PEP 695 type parameter syntax and all modern typing features
- Provides detailed diagnostic messages with fix suggestions
- Full Language Server Protocol support for IDE integration beyond VS Code

## Comparison with Similar Tools
- **mypy** — the original Python type checker, slower but with a broader plugin ecosystem
- **pytype** — Google's type checker with automatic type inference and rewriting
- **Pyre** — Meta's type checker focused on large monorepos with incremental analysis
- **Ruff** — ultrafast linter and formatter but does not perform type checking
- **Pylint** — general-purpose linter that catches code smells but not type errors

## FAQ
**Q: Can I use Pyright alongside mypy?**
A: Yes. Many teams run both in CI. Pyright and mypy may flag different issues due to differing inference strategies, so overlapping coverage can catch more bugs.

**Q: Does Pyright replace Pylance?**
A: Pylance is a VS Code extension that bundles Pyright as its type-checking engine and adds IDE features like auto-imports and semantic highlighting. Pyright is the standalone CLI.

**Q: How do I migrate a project from mypy to Pyright?**
A: Replace the mypy config with a `pyrightconfig.json`, run Pyright, and address any new diagnostics. Most PEP 484 annotations are fully compatible between the two.

**Q: Does Pyright work with Django and other dynamic frameworks?**
A: Pyright handles most Django patterns when paired with django-stubs type stubs. Highly dynamic code may need targeted `# type: ignore` annotations.

## Sources
- https://github.com/microsoft/pyright
- https://microsoft.github.io/pyright/

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Source: https://tokrepo.com/en/workflows/be729969-442b-11f1-9bc6-00163e2b0d79
Author: Script Depot