生成另一个包含原始类的类的类的通用 TypeVar 解决方案

Question

我正在尝试提出一个通用的

TypeVar

解决方案，以避免创建不断扩展的

Union

类型注释。这是我目前所拥有的有点人为的 MRE：

from __future__ import annotations
from typing import Union

class CreatedDetails:
    def __init__(self, creator: Union[Creator1, Creator2], new: bool) -> None:
        self.creator = creator
        self.new = new

class Creator1:
    def __init__(self) -> None:
        self.name = "creator1"

    def create(self) -> CreatedDetails:
        return CreatedDetails(creator=self, new=True)

class Creator2:
    def __init__(self) -> None:
        self.name = "creator2"

    def create(self) -> CreatedDetails:
        return CreatedDetails(creator=self, new=False)

creator1 = Creator1()
created = creator1.create()
created.creator.name

这很不错，我的类型检查器可以识别一切：

但是，这依赖于我向

Creator

类型注释添加新的

Ùnion

类。

我尝试过使用通用的

TypeVar

：

from __future__ import annotations
from typing import TypeVar

CreatorRecord = TypeVar("CreatorRecord")

class CreatedDetails:
    def __init__(self, creator: CreatorRecord, new: bool) -> None:
        self.creator = creator
        self.new = new

class Creator:
    pass

class Creator1(Creator):
    def __init__(self) -> None:
        self.foo = "foo"

    def create(self) -> CreatedDetails:
        return CreatedDetails(creator=self, new=True)

class Creator2(Creator):
    def __init__(self) -> None:
        self.bar = "bar"

    def create(self) -> CreatedDetails:
        return CreatedDetails(creator=self, new=False)

creator1 = Creator1()
created = creator1.create()
created.creator.foo
created.new

但是，类型检查器并不能完全识别这一点：

我哪里出错了？

Answer 1

CreatedDetails

本身必须是通用的。如果类型检查器只知道

created

是

CreatedDetails

的实例，则不足以告诉创建它的创建者的特定类型。但通过正确的注释，

CreatedDetails[Creator1]

类型可以提供该信息。

您已经创建了一个泛型构造函数，但您真正需要的是一个泛型类：

from typing import TypeVar, Generic
Creator = TypeVar("Creator")

class CreatedDetails(Generic[Creator]):
    creator: Creator
    new: bool
    def __init__(self, creator: Creator, new: bool) -> None:
        self.creator = creator
        self.new = new

class Creator1:
    def __init__(self) -> None:
        self.foo = "foo"

    def create(self) -> CreatedDetails['Creator1']:
        return CreatedDetails(creator=self, new=True)

class Creator2:
    def __init__(self) -> None:
        self.bar = "bar"

    def create(self) -> CreatedDetails['Creator2']:
        return CreatedDetails(creator=self, new=False)