generics_self_attributes error

Incompatible type for Self-typed attribute

When a class declares an attribute annotated with Self (or Self | None, OptionalSelf, etc.), that attribute's type is bound to the concrete subclass at each usage site. Passing or assigning a parent-class instance where the subclass is expected is a type error.

from typing import Self, TypeVar, Generic
from dataclasses import dataclass

T = TypeVar("T")

@dataclass
class LinkedList(Generic[T]):
    value: T
    next: Self | None = None

@dataclass
class OrdinalLinkedList(LinkedList[int]):
    def ordinal_value(self) -> str:
        return str(self.value)

xs = OrdinalLinkedList(value=1, next=LinkedList[int](value=2))  # E
xs.next = LinkedList[int](value=3, next=None)                  # E

Specification: <https://typing.readthedocs.io/en/latest/spec/generics.html#use-in-attribute-annotations>

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial generics_self_attributes down per-file or per-path from your editor or pyproject.toml, or fix the code so it type-checks. See the Type System rules and the complete diagnostic reference.

Canonical URL: https://www.basilisk-python.dev/errors/generics_self_attributes