返回 self 的 python 通用属性用法的返回值类型不兼容

Question

尝试实现尊重mypy的节点和树 inheritance 层次结构，我有下一个类：

from __future__ import annotations
import dataclasses
from typing import Generic, TypeVar, Optional

GenericNodeValue = TypeVar('GenericNodeValue')

@dataclasses.dataclass
class BaseNode(Generic[GenericNodeValue]):
    value: GenericNodeValue
    parent: Optional[BaseNode] = None
    left: Optional[BaseNode] = None
    right: Optional[BaseNode] = None

    @property
    def dummy(self) -> BaseNode:
        return self

GenericNode = TypeVar('GenericNode', bound=BaseNode)

class BaseTree(Generic[GenericNode]):
    def __init__(self):
        self.root: Optional[GenericNode] = None

    def get_dummy(self, node: GenericNode) -> GenericNode:
        return node.dummy

@dataclasses.dataclass
class RedBlackTreeNode(BaseNode[int]):
    red: bool = False

class RedBlackTree(BaseTree[RedBlackTreeNode]):
    def get_dummy2(self, node: RedBlackTreeNode) -> RedBlackTreeNode:
        return node.dummy

但mypy返回错误：

test.py:29: error: Incompatible return value type (got "BaseNode[Any]", expected "GenericNode")
test.py:39: error: Incompatible return value type (got "BaseNode[Any]", expected "RedBlackTreeNode")

有什么方法可以使用 python 输入来实现我的逻辑吗？

Answer 1

诀窍是向self参数添加注释。 例如：

T = TypeVar('T')
V = TypeVar('V', bound='BaseNode')

@dataclasses.dataclass
class BaseNode(Generic[T]):
    value: T
    parent: Optional[BaseNode[T]] = None
    left: Optional[BaseNode[T]] = None
    right: Optional[BaseNode[T]] = None

    @property
    def dummy(self: V) -> V:
        return self

    @property
    def dummy_parent(self: V) -> V:
        assert isinstance(self.parent, type(self))
        return self.parent

顺便说一句，您应该将类型参数添加到可选属性中，这样它们就不会变成BaseNode[Any] ，失去泛型的好处！