00hello.py

def hello(name: str) -> None:
    pass

01hello-annotated.py

from typing_extensions import Annotated


class Description:
    def __init__(self, description: str) -> None:
        self.description = description


def hello(*, name: Annotated[str, Description("the name of person")]) -> None:
    print(f"hello {name}")

02reveal-type.py

from typing_extensions import Annotated


class Description:
    def __init__(self, description: str) -> None:
        self.description = description


def hello(*, name: Annotated[str, Description("the name of person")]) -> None:
    reveal_type(name)
    print(f"hello {name}")

03extract-metadata.py

from typing_extensions import Annotated


class Description:
    def __init__(self, description: str) -> None:
        self.description = description


def hello(*, name: Annotated[str, Description("the name of person")]) -> None:
    print(f"hello {name}")


if __name__ == "__main__":
    from typing_extensions import get_type_hints

    print(get_type_hints(hello))
    # {'name': <class 'str'>, 'return': <class 'NoneType'>}

    print(get_type_hints(hello, include_extras=True))
    # {'name': typing_extensions.Annotated[str, <__main__.Description object at 0x10cd1e730>], 'return': <class 'NoneType'>}

    from typing_extensions import get_args, get_origin

    hints = get_type_hints(hello, include_extras=True)
    print(get_args(hints["name"]))
    # (<class 'str'>, <__main__.Description object at 0x106427730>)

    print(get_origin(hints["name"]))
    # <class 'typing_extensions.Annotated'>

04extract-metadata.py

from typing_extensions import Annotated


class Description:
    def __init__(self, description: str) -> None:
        self.description = description


def hello(*, name: Annotated[str, Description("the name of person")]) -> None:
    print(f"hello {name}")


if __name__ == "__main__":
    from typing_extensions import get_type_hints

    hints = get_type_hints(hello, include_extras=True)

    import typing_inspect

    print(typing_inspect.get_args(hints["name"]))
    # (<class 'str'>,)

    print(hasattr(hints["name"], "__metadata__"))
    # True
    print(hints["name"].__metadata__)
    # (<__main__.Description object at 0x104b9b730>,)

Makefile

PY_FILE = $(shell echo $@*.py)

00:
	mypy --strict $(PY_FILE)
01:
	mypy --strict $(PY_FILE)
02:
	diff -u 01*.py 02*.py || exit 0
	mypy --strict $(PY_FILE)

setup:
	python -m pip install -r requirements.txt

requirements.txt

typing-extensions
typing-inspect