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Introduction

Mypy is a static type checker for Python 3 and Python 2.7. If you sprinkle your code with type annotations, mypy can type check your code and find common bugs. As mypy is a static analyzer, or a lint-like tool, the type annotations are just hints for mypy and don't interfere when running your program. You run your program with a standard Python interpreter, and the annotations are treated effectively as comments.

Using the Python 3 function annotation syntax (using the PEP 484 notation) or a comment-based annotation syntax for Python 2 code, you will be able to efficiently annotate your code and use mypy to check the code for common errors. Mypy has a powerful and easy-to-use type system with modern features such as type inference, generics, callable types, tuple types, union types, and structural subtyping.

As a developer, you decide how to use mypy in your workflow. You can always escape to dynamic typing as mypy's approach to static typing doesn't restrict what you can do in your programs. Using mypy will make your programs easier to understand, debug, and maintain.

This documentation provides a short introduction to mypy. It will help you get started writing statically typed code. Knowledge of Python and a statically typed object-oriented language, such as Java, are assumed.

Note

Mypy is used in production by many companies and projects, but mypy is officially beta software. There will be occasional changes that break backward compatibility. The mypy development team tries to minimize the impact of changes to user code.