arg_dataclasses.py

import argparse
import dataclasses
from typing import TypeVar, Generic, Type

T = TypeVar("T")


class Parser(Generic[T]):
    def __init__(self, cls: Type[T]) -> None:
        assert dataclasses.is_dataclass(cls)
        self.cls = cls
        self.parser = make_parser(cls)

    def parse_args(self, args=None) -> T:
        args = self.parser.parse_args(args)
        return self.make_instance(vars(args))

    def make_instance(self, d):
        return self.cls(**d)


def make_parser(cls: Type[T]) -> argparse.ArgumentParser:
    parser = argparse.ArgumentParser()
    for f in dataclasses.fields(cls):
        opt_name = f"--{f.name}"
        default = None if f.default == dataclasses.MISSING else f.default
        parser.add_argument(opt_name, type=f.type, default=default)
    return parser


@dataclasses.dataclass
class WebOpt:
    port: int = dataclasses.field(default=8080)
    host: str = dataclasses.field(default="0.0.0.0")


def serve(opt: WebOpt) -> None:
    print(f"serve on {opt.host}:{opt.port}")


def main() -> None:
    parser = Parser(WebOpt)
    args = parser.parse_args()
    serve(args)


if __name__ == "__main__":
    main()