from typing import Any, Optional
from pydantic import BaseModel, PrivateAttr


class BadBase(BaseModel):
    _random: Optional[str] = PrivateAttr(None)


class OkBase(BaseModel):
    random: Optional[str] = None


class DoesNotWork(BadBase):
    a: str
    _b: Optional[str] = PrivateAttr(None)

    def model_post_init(self, __context: Any) -> None:
        self._b = "cool"
        return super().model_post_init(__context)


class Works(OkBase):
    a: str
    _b: Optional[str] = PrivateAttr(None)

    def model_post_init(self, __context: Any) -> None:
        self._b = "cool"
        return super().model_post_init(__context)


if __name__ == "__main__":
    a_dict = {"a": "string"}
    bad_model = DoesNotWork.model_validate(a_dict)
    good_model = Works.model_validate(a_dict)
    assert bad_model._b is None  # should be "cool"
    print(bad_model._b)
    assert good_model._b == "cool"
    print(good_model._b)