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 four things:

exposes utilities that allow to inspect C3-linearized MROs of runtime generics and type-check them with variance support: get_mro(), type_check();
makes it possible to retrieve the type arguments passed to the generic class at runtime before the class was instantiated: get_type_arguments(), get_alias();
offers facilities to find how parent classes are parametrized ( e.g. if Foo[T] inherits from Dict[str, T], finds that Dict[str, int] is a parent for Foo[int] ): get_parents();
given a parametrized generic class (generic alias), makes every class method use generic alias cls instead of the origin class (unless decorated with @no_alias).

A Simple Example

3.12+ (PEP 695 syntax):

from __future__ import annotations

import io
from typing import TYPE_CHECKING

from runtime_generics import get_alias, get_type_arguments, runtime_generic, type_check

if TYPE_CHECKING:
    from typing import IO, Literal, overload


@runtime_generic
class IOWrapper[T: str | bytes]:
    data_type: type[T]

    def __init__(self, stream: IO[T]) -> None:
        (self.data_type,) = get_type_arguments(self)
        self.stream = stream

    if TYPE_CHECKING:
        @overload
        def is_binary(self: IOWrapper[bytes]) -> Literal[True]: ...

        @overload
        def is_binary(self: IOWrapper[str]) -> Literal[False]: ...

    def is_binary(self) -> bool:
        # alternatively here: `self.data_type == bytes`
        return type_check(self, IOWrapper[bytes])

    def __repr__(self) -> str:
        return f"<{get_alias(self)} object at ...>"


my_binary_data = IOWrapper[bytes](io.BytesIO(b"foo"))
assert my_binary_data.data_type is bytes
assert my_binary_data.is_binary()
assert repr(IOWrapper[str](io.StringIO())) == "<__main__.IOWrapper[str] object at ...>"

3.8+:

from __future__ import annotations

import io
from typing import TYPE_CHECKING, Generic, TypeVar

from runtime_generics import get_alias, get_type_arguments, runtime_generic, type_check

if TYPE_CHECKING:
    from typing import IO, Literal, overload

T = TypeVar("T", str, bytes)


@runtime_generic
class IOWrapper(Generic[T]):
    data_type: type[T]

    def __init__(self, stream: IO[T]) -> None:
        (self.data_type,) = get_type_arguments(self)
        self.stream = stream

    if TYPE_CHECKING:
        @overload
        def is_binary(self: IOWrapper[bytes]) -> Literal[True]: ...

        @overload
        def is_binary(self: IOWrapper[str]) -> Literal[False]: ...

    def is_binary(self) -> bool:
        # alternatively here: `self.data_type == bytes`
        return type_check(self, IOWrapper[bytes])

    def __repr__(self) -> str:
        return f"<{get_alias(self)} object at ...>"


my_binary_data = IOWrapper[bytes](io.BytesIO(b"foo"))
assert my_binary_data.data_type is bytes
assert my_binary_data.is_binary()
assert repr(IOWrapper[str](io.StringIO())) == "<__main__.IOWrapper[str] object at ...>"

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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.

Fork the runtime_generics repository on GitHub.
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
```

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! ❤️

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