ABC's with Final Attributes

[nicwest]

I'm trying to understand why pyright doesn't like this.

from abc import ABC

class Point:
    x: int

    def __init__(self) -> None:
        self.x = 1

class BasePoint(ABC):
    x: int

class SubPoint(BasePoint):

    def __init__(self) -> None:
        self.x = 1

class ImmutablePoint:
    x: Final[int]

    def __init__(self) -> None:
        self.x = 1

class BaseImmutablePoint(ABC):
    x: Final[int]      # "x" is declared Final, but value is not assigned


class SubImmutablePoint(BaseImmutablePoint):
    def __init__(self) -> None:
        self.x = 1     # "x" cannot be redeclared because parent class "BaseImmutablePoint" declares it as Final

I would expect the last two variations to be consistent with the non ABC/final variations

[erictraut]

Pyright is following the typing spec in this case. Mypy produces the same results.

Please refer to the this section of the spec for information about Final.

The ABC variant you've defined here is not equivalent to the non-ABC variant. In the non-ABC variant, you've used Final in the subclass. In the ABC variant, you've used Final in the parent class, and you've failed to provide a value for it — and then overridden its value in the subclass.

Perhaps the draft PEP 767 provides the functionality you're looking for here.