mypy-pure 0.1.0

A mypy plugin that adds support for checking pure functions.

mypy-pure

A mypy plugin that enforces purity in Python functions.

Disclaimer

This project has been created using the support of the following AI tools:

• ChatGPT
• Antigravity (Gemini)

After that, it has been manually reviewed and fixed.

What is a Pure Function?

A pure function is a function that has the following properties:

1. Deterministic: Its return value is the same for the same arguments.
2. No Side Effects: It does not cause any observable side effects (e.g., modifying global variables, I/O operations, database writes).

This mypy plugin helps enforcing statically the second property by detecting calls to known impure functions within functions decorated with @pure.

Installation

Install:

pip install mypy-pure

Enable it in your mypy.ini:

[mypy]
plugins = mypy_pure.plugin

Usage

Pure function (no side-effects):

from mypy_pure.decorators import pure

@pure
def add(x: int, y: int) -> int:
    return x + y

Impure function (with side-effects):

import os
from mypy_pure.decorators import pure

@pure
def bad() -> None:
    os.remove("file.txt")

Configuration

You can configure additional impure functions in your mypy.ini file:

[mypy-pure]
impure_functions = my_module.impure_func, another_module.bad_func