No "post-init only" marker

[AJR1991]

I want to use slots in CPython using dataclassy, but I also want to be able to hide initializers for certain variables from the user. For example:

@dataclass(slots=True)
class TestDataClass:
    normal: float
    _hidden: str = post_init("Test") 
    _post: float = post_init()

    def __post_init__(self):
        self._post = 3.141 * self.normal * self.normal

What I'm doing here is making _hidden and _post unable to be initialized as part of the given args on construction (meaning you can't set it via _hidden="hello") . It's possible to do this kind of thing without slots by just initializing it in __post_init__ but with slots, you can't without having to define __slots__ at the top, which looks ugly.

Is it possible to add this functionality? Or am I misreading documentation and this is already possible?

[biqqles]

No, it's not already possible. I originally didn't want to implement something like late_init (taking the name from Kotlin) because I think it means checking the type before generating __init__ which we don't do for anything else, so it would be messy. Even factory is implemented without needing to do this. I also thought it was neat just to be able to simply assign attributes in __post_init__. That said it never occurred to me that missing it out would be a problem for slotted classes.

I need to think about this more to work out how best to implement the feature.