runtime_generics

Highly into type-safe Python code?

runtime_generics is a niche Python library that allows you to reuse type arguments explicitly passed at runtime to generic classes before instantiation.

The library does three things:

• makes it possible to retrieve the type arguments passed to the generic class at runtime before the class was instantiated;
• given a parametrized generic class (generic alias), it makes every class method use generic alias cls instead of the origin class;
• offers facilities to find how parent classes are parametrized, so e.g. if Foo[T] inherits from Dict[str, T], find that Dict[str, int] is a parent for Foo[int].

A simple example

3.12+ (PEP 695 syntax):

from runtime_generics import get_type_arguments, runtime_generic

@runtime_generic
class MyGeneric[T]:
    type_argument: type[T]

    def __init__(self) -> None:
        (self.type_argument,) = get_type_arguments(self)

    @classmethod
    def whoami(cls) -> None:
        print(f"I am {cls}")

my_generic = MyGeneric[int]()
assert my_generic.type_argument is int
my_generic.whoami()  # I am MyGeneric[int]

3.8+:

from __future__ import annotations

from typing import Generic, TypeVar
from runtime_generics import get_type_arguments, runtime_generic

T = TypeVar("T")

@runtime_generic
class MyGeneric(Generic[T]):
    type_argument: type[T]

    def __init__(self) -> None:
        (self.type_argument,) = get_type_arguments(self)

    @classmethod
    def whoami(cls) -> None:
        print(f"I am {cls}")

my_generic = MyGeneric[int]()
assert my_generic.type_argument is int
my_generic.whoami()  # I am MyGeneric[int]

Installation

You might simply install it with pip:

pip install runtime-generics

If you use Poetry, then you might want to run:

poetry add runtime-generics

For contributors

[!Note] If you use Windows, it is highly recommended to complete the installation in the way presented below through WSL2.

1. Fork the runtime_generics repository on GitHub.

2. Install Poetry.
   Poetry is an amazing tool for managing dependencies & virtual environments, building packages and publishing them. You might use pipx to install it globally (recommended):

   pipx install poetry
   

   _{If you encounter any problems, refer to the official documentation for the most up-to-date installation instructions.}

   Be sure to have Python 3.8 installed—if you use pyenv, simply run:

   pyenv install 3.8
   

3. Clone your fork locally and install dependencies.

   git clone https://github.com/your-username/runtime_generics path/to/runtime_generics
   cd path/to/runtime_generics
   poetry env use $(cat .python-version)
   poetry install
   

   Next up, simply activate the virtual environment and install pre-commit hooks:

   poetry shell
   pre-commit install
   

For more information on how to contribute, check out CONTRIBUTING.md.
Always happy to accept contributions! ❤️

Legal info

© Copyright by Bartosz Sławecki (@bswck).
This software is licensed under the terms of MIT License.