Mypy is a static type checker for Python that helps developers identify programming errors before executing their code. It examines type annotations and how values are used throughout a program, reporting inconsistencies that might otherwise be discovered only during testing or production use.
The application is designed around gradual typing. Developers can introduce annotations into selected parts of a program while leaving other areas dynamically typed, allowing type checking to be adopted without rewriting an entire codebase.
Mypy is particularly valuable in larger projects where interfaces between modules and libraries can become difficult to manage. By checking expectations about function arguments, return values and object types, it helps make program behaviour easier to reason about while providing additional safeguards during refactoring.
This is free and open source software.
Key Features
- Supports standard Python type annotations, generics, union types and callable types.
- Provides structural subtyping through protocols, allowing compatibility without explicit inheritance.
- Offers configurable strict checking modes and fine-grained control over diagnostic categories.
- Infers types where possible, reducing the need for annotations on every local variable.
- Uses incremental caching to avoid repeatedly analysing unchanged modules.
- Includes a long-running daemon with fine-grained dependency tracking for faster repeated checks.
- Supports third-party type stubs for libraries that do not provide their own annotations.
- Offers a plugin system for libraries with specialised typing behaviour.
- Integrates with compatible development editors and automated checking pipelines.
Website: github.com/python/mypy
Support:
Developer: Jukka Lehtosalo and contributors
License: MIT License
mypy is written in Python. Learn Python with our recommended free books and free tutorials.
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