Tips: I strongly recommend you to read Algebraic Effects for the Rest of Us before you start.

Affection is a small library that implements Algebraic Effect for Python. It leverages asyncio, decorator and with syntax for a smooth experience.

Warning: Please note that until Higher Rank Type Variants are supported in Python, the Effect.handle API will be quite ugly.

Usage

This project is designed to be a single file project.

You can either directly copy it into your project, or add affection from PyPI with your favorite package manager.

from affection import Effect, Handle, effect, perform


class Log(Effect[None]):
    def __init__(self, content: str):
        self.content = content


def get_name(name: str | None = None) -> str:
    perform(Log(f"Getting name with {name}"))
    return perform(effect("ask_name", str)) if name is None else name


def main():
    with Handle() as h:

        @Log.handle(h)
        def _(l: Log):
            print(l.content)

        @effect("ask_name", str).handle(h)
        def _(_) -> str:
            return "Default"

        perform(Log("Test parent log"))

        with Handle() as i_h:
            @Log.handle(h)
            def _(l: Log):
                print("Inner", l.content.lower())
            print(get_name("Ann"))
            print(get_name())

if __name__ == "__main__":
    main()
    """
    Test parent log
    Inner getting name with ann
    Ann
    Inner getting name with none
    Default
    """