尝试注释哈希变量时，“ABCMeta"对象不可下标 [英] 'ABCMeta' object is not subscriptable when trying to annotate a hash variable

问题描述

以下dataclass:

from abc import ABC
from collections.abc import Mapping
from dataclasses import dataclass, field

@dataclass(eq=True, order=True, frozen=True)
class Expression(Node, ABC):
    def node(self):
        raise NotImplementedError

用作基类:

@dataclass(eq=True, frozen=True)
class HashLiteral(Expression):
    pairs: Mapping[Expression, Expression]
    ...

Node 定义为:

@dataclass(eq=True, frozen=True)
class Node:
    def __str__(self) -> str:
        raise NotImplementedError

尝试使用 HashLiteral 类时出现错误:

When trying to use the HashLiteral class I get the error:

pairs: Mapping[Expression, Expression]
TypeError: 'ABCMeta' object is not subscriptable

我上面的 pairs 注释有什么问题?

What is wrong with my annotation of pairs above?

推荐答案

您应该使用 typing.Mapping 而不是 collections.abc.Mapping.typing 包含各种类型的许多通用版本，旨在用于类型提示.根据 mypy 文档，存在一些差异typing 类和 collections.abc 类之间的区别，但他们不清楚这些区别到底是什么.

You should use typing.Mapping instead of collections.abc.Mapping. typing contains many generic versions of various types, which are designed to be used in type hints. According to the mypy documentation, there are some differences between the typing classes and the collections.abc classes, but they're unclear on exactly what those differences are.

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