Make dataclass props initializable

props_to_init.py

from dataclasses import field, dataclass
import datetime
from functools import wraps


def props_to_init(additional_kwargs):
    def decorator(cls):
        def modify_init(init):
            @wraps(init)
            def __init__(self, **kwargs):
                kwargs_without_properties = {
                    k: v for k, v in kwargs.items() if k not in additional_kwargs.keys()
                }
                init(
                    self,
                    **kwargs_without_properties,
                )
                for k, v in additional_kwargs.items():
                    setattr(self, k, v() if callable(v) else v)

            return __init__

        cls.__init__ = modify_init(cls.__init__)
        return cls

    return decorator


@props_to_init({"date": datetime.datetime.now})
@dataclass
class Config:
    secret: dict[str, str] = field(default_factory=lambda: {}, repr=False)
    date_slice: str = field(init=False, repr=False, default="")

    # `date` is added to the `init` fields, see decorators
    # __date is to provide the source of truth for property getter / setter
    __date: datetime.datetime = field(
        init=False, repr=False, default_factory=datetime.datetime.now
    )

    def __post_init__(self):
        self.__date = self.date
        self.date_slice = self.__date.strftime("%Y%m%d")

    @property
    def date(self) -> datetime.datetime:
        return self.__date

    @date.setter
    def date(self, date: datetime.datetime) -> None:
        self.__date = date
        self.date_slice = self.__date.strftime("%Y%m%d")


t = Config(date=datetime.datetime(2021, 1, 1), secret={"user": "xyz"})
print(t.date_slice)
t.date = datetime.datetime(2022, 1, 2)
print(t.date_slice)
print(t.secret)
print(t.date)