typed_classproperties

Typed decorators for classproperty and cached_classproperty.

Python 3 compatible only. No dependenciesfootnote:[The library [typing_extensions](https://github.com/python/typing_extensions) is required when running with a Python version less than 3.12].

Installation

This package is hosted on PyPI and can be installed using uv or pip.

Add to your uv project/script’s dependencies

uv add typed_classproperties

Install using pip after creating a virtual environment

path/to/venv/python -m pip install typed_classproperties

Example Usage

from typing import override

from typed_classproperties import classproperty, cached_classproperty


class Foo:
    @override
    def __init__(self, bar: str) -> None:
        self.bar: str = bar

    @classproperty
    def BAR(cls) -> int:
        return 1


assert Foo.BAR == 1
assert Foo(bar="one").BAR == 1


class CachedFoo:
    @override
    def __init__(self, bar: str) -> None:
        self.bar: str = bar

    @cached_classproperty
    def BAR(cls) -> int:
        print("This will be executed only once")
        return 1


assert CachedFoo.BAR == 1
assert CachedFoo(bar="bar").FOO == 1

Supported Type-Checkers

This package makes use of some reasonably advanced Python functionality that could be considered a hack. The appropriate solution to correctly annotate the types matching the runtime behaviour of classproperties is explained in PEP767. This PEP, however, is still in draft and not yet accepted; therefore, not all type checkers are supported.

While we will attempt to fix type annotation bugs in this project for alternative type-checkers, our focus is on the following officially supported type checkersfootnote:[The list of officially supported type checkers is subject to change between any minor version release]:

• mypy
• ty ≤ 0.0.59footnote:[Support for ty is capped to below 0.0.60, which began to find type-errors with the hacks used in this project]

❗ IMPORTANT
Patches to fix bugs in this project for alternative type-checkers are welcome and much appreciated!

Tests

See tests.py for further usage examples and expected behaviour.

To run tests

uv run --group test -- pytest

Credits

Credits to Denis Ryzhkov, on Stack Overflow, for the original implementation of the @classproperty decorator: https://stackoverflow.com/a/13624858/1280629