auto-typing-final

Auto-fixer for Python code that adds typing.Final annotation to variable assignments inside functions that are not reassigned, and removes the annotation from variables that are mutated.

 def foo() -> None:
-    a = 2
+    a: typing.Final = 2

-    b: typing.Final = 2
+    b = 2
     b = 3

Basically, this, but handles different operations (like usage of nonlocal, augmented assignments: +=, etc) as well.

• Keeps type checker happy.
• Adds global import if it's not imported yet (import typing/from typing import Final).
• Inspects one file at a time.
• Is careful with global variables: adds Final only for uppercase variables, ignores variable that are referenced in global statement inside functions in current file, and avoids removing Final when it already was set (docs).
• Ignores class variables: it is common to use typing.ClassVar instead of typing.Final.

How To Use

Having uv installed:

uvx auto-typing-final .

or:

pipx run auto-typing-final .

Options

You can specify --check flag to check the files instead of actually fixing them:

auto-typing-final . --check

Also, you can choose import style from two options: typing-final (default) and final:

auto-typing-final . --import-style typing-final

• typing-final enforces import typing and typing.Final,
• final enforces from typing import Final and Final.

Also, you can set --ignore-global-vars flag to ignore global variables:

auto-typing-final . --ignore-global-vars

Ignore comment

You can ignore variables by adding # auto-typing-final: ignore comment to the line (docs).

VS Code Extension

The extension uses LSP server bundled with the CLI (executable name is auto-typing-final-lsp-server). To get started, add auto-typing-final to your project:

uv add auto-typing-final --dev

After that, install the extension: https://marketplace.visualstudio.com/items?itemName=vrslev.auto-typing-final. In Python environments that have auto-typing-final installed, extension will be activated automatically.

Settings

• Import style can be configured in settings: "auto-typing-final.import-style": "typing-final" or "auto-typing-final.import-style": "final".
• Ignore global variables can be configured in settings: "auto-typing-final.ignore-global-vars": true.

Notes

Library code of currently activated environment will be ignored (for example, .venv/bin/python is active interpreter, all code inside .venv will be ignored).