python dect键和值在哪里取决于相同的通用类型

Question

我想定义一个键，其键和值共享相同的通用类型，并且对其有一些约束。以下是这种情况的例子。但是，将mypy应用于以下代码会导致错误：

tmp.py:8: error: Type variable "tmp.AT" is unbound
tmp.py:8: note: (Hint: Use "Generic[AT]" or "Protocol[AT]" base class to bind "AT" inside a class)
tmp.py:8: note: (Hint: Use "AT" in function signature to bind "AT" inside a function)
Found 1 error in 1 file (checked 1 source file)

如何解决此问题？ 我之所以需要这样的命令的原因是我想在dict的钥匙和价值之间添加类型约束。

tmp.py：

from typing import Dict, Generic, TypeVar, Type, List

class A: pass
class B(A): pass
class C(A): pass

AT = TypeVar("AT", bound=A)
d: Dict[Type[AT], List[AT]] = {}

Answer 1

我最终通过定义从dict继承的自定义dict来避免此问题。

from typing import Dict, TypeVar, Type, List
from dataclasses import dataclass

AT = TypeVar("AT")

class ConstrainedDict(Dict):
    def __getitem__(self, k: Type[AT]) -> List[AT]:
        return super().__getitem__(k)

class Foo: pass
class Bar: pass

d: ConstrainedDict
a: List[Foo] = d[Foo]  # expected to pass
b: List[Foo] = d[Bar]  # expected to cause error

Mypy的结果是我预期的：

tmp.py:15: error: Invalid index type "Type[Bar]" for "ConstrainedDict"; expected type "Type[Foo]"
Found 1 error in 1 file (checked 1 source file)