Support add_argument type parameter about datargs

[roee30]

datargs is meant to express a simple equivalence between dataclasses and argument parsers so it is not meant for this use. If you can reuse the dataclass, you can also reuse the same utility functions - setting the log level, just converting between the parser dataclass and a slightly different one, or whatever else you choose.

Note that you can create a custom class to mimic argparse's behavior, although I would generally advise against it:

from dataclasses import dataclass
import datargs
import logging


class Level(int):
    def __new__(cls, level):
        try:
            return logging._nameToLevel[level]
        except KeyError:
            raise TypeError(f'invalid logging level {level}')


@dataclass
class Args:
    level: Level


print(datargs.parse(Args, ['--level', 'DEBUG']))

This should work properly both at runtime and with static type checking.