Simple dataclass that auto-implements slots

dataclass.py

from typing import TypeVar

T_ = TypeVar("T_", bound=object)


def myDataClass(cls: T_) -> T_:
    """A simple data class decorator that generates slots automatically
    and creates an init function to match.
    """

    def wrap(cls: T_) -> T_:
        fields = tuple(a for a in dir(cls) if not a.startswith("__"))
        values = {a: getattr(cls, a) for a in fields}

        def init(self: T_) -> None:
            nonlocal values
            for a, v in values.items():
                setattr(self, a, v)

        return type(cls.__class__.__name__, (object,), {  # type: ignore
            "__slots__": fields, "__init__": init
        })

    return wrap(cls)


# With this decorator, the following class:

@myDataClass
class A:

    one = 1
    two = "2"


# Becomes:

class B:

    __slots__ = ("one", "two")

    def __init__(self) -> None:
        self.one = 1
        self.two = "2"