递归类型注解 [英] Recursive type annotations

问题描述

我正在尝试在适用的情况下向我的代码库引入静态类型注释.一种情况是在读取 JSON 时，结果对象将是一个以字符串为键的字典，具有以下类型之一的值:

I'm trying to introduce static type annotations to my codebase where applicable. One case is when reading a JSON, the resulting object will be a dictionary keyed by strings, with values of one of the following types:

• bool
• str
• 浮动
• int
• list
• dict

然而，上面的 list 和 dict 可以包含相同类型的字典，导致递归定义.这在 Python3 的类型结构中可以表示吗?

However the list and dict above can contain that same sort of dictionary, leading to a recursive definition. Is this representable in Python3's type structure?

推荐答案

从 mypy 0.641 开始，mypy 不支持您正在寻找的那种递归类型注释.自然语法:

As of mypy 0.641, mypy doesn't support the sort of recursive type annotation you're looking for. The natural syntax:

from typing import Union, Dict, List

JSONVal = Union[None, bool, str, float, int, List['JSONVal'], Dict[str, 'JSONVal']]

d: JSONVal = {'a': ['b']}

产生错误报告缺乏递归类型支持:

produces an error reporting a lack of recursive type support:

$ mypy asdf.py
asdf.py:3: error: Recursive types not fully supported yet, nested types replaced with "Any"

另请参阅关于递归类型支持的 mypy 问题跟踪器线程.

Also see the mypy issue tracker thread on recursive type support.

就目前而言，Dict[str, Any] 可能是要走的路.

For now, Dict[str, Any] is probably the way to go.

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