Mypy: Optional Static Typing for Python

1.19.1 · active · verified Sat Mar 28

Mypy is a static type checker for Python, enabling optional static typing to improve code quality and maintainability. As of version 1.19.1, it supports Python 3.9 and later, with regular updates and a stable release cadence.

Warnings

breaking Mypy 1.9 introduced breaking changes due to an updated typeshed version, dropping support for Python 3.7.
Fix: Upgrade to Python 3.8 or later to maintain compatibility.
gotcha Using 'Final' and 'TypedDict' from 'typing' requires Python 3.8 or later; for earlier versions, install 'typing_extensions'.
Fix: Install 'typing_extensions' to use these features on older Python versions.

Install

pip install mypy Install Mypy

Imports

Final
```
from typing import Final
```
Use 'Final' from 'typing' to indicate constants; 'typing_extensions' is needed for Python versions prior to 3.8.
TypedDict
```
from typing import TypedDict
```
Use 'TypedDict' from 'typing' for defining typed dictionaries; 'typing_extensions' is needed for Python versions prior to 3.8.

Quickstart

Integrate Mypy into your Python application by importing 'mypy.api' and calling the 'run' function with command-line arguments. This allows programmatic access to Mypy's type checking capabilities.

import sys
from mypy import api

result = api.run(sys.argv[1:])

if result[0]:
    print('\nType checking report:\n')
    print(result[0])  # stdout

if result[1]:
    print('\nError report:\n')
    print(result[1])  # stderr

sys.exit(result[2])  # exit status

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