如何在 NamedTuple 中键入函数属性

发布于 2025-01-16 08:24:10 字数 751 浏览 2 评论 0原文

我有一段像

from typing import Callable, NamedTuple, TypeVar


def f1(x: int) -> int:
    return x


def f2(y: str) -> int:
    return len(y)


T = TypeVar("T", int, str)


class Config(NamedTuple):
    func: Callable[[T], int]


c1 = Config(func=f1)
c2 = Config(func=f2)

Mypy 抱怨的代码：

toy.py:19:18: error: Argument "func" to "Config" has incompatible type "Callable[[int], int]"; expected "Callable[[Config], int]"
toy.py:20:18: error: Argument "func" to "Config" has incompatible type "Callable[[str], int]"; expected "Callable[[Config], int]"
Found 2 errors in 1 file (checked 1 source file)

为什么它会期望 "Callable[[Config], int]"?

我正在使用 Python-3.8，并且 mypy==0.800

原文

I have a piece of code like

from typing import Callable, NamedTuple, TypeVar


def f1(x: int) -> int:
    return x


def f2(y: str) -> int:
    return len(y)


T = TypeVar("T", int, str)


class Config(NamedTuple):
    func: Callable[[T], int]


c1 = Config(func=f1)
c2 = Config(func=f2)

Mypy complains:

toy.py:19:18: error: Argument "func" to "Config" has incompatible type "Callable[[int], int]"; expected "Callable[[Config], int]"
toy.py:20:18: error: Argument "func" to "Config" has incompatible type "Callable[[str], int]"; expected "Callable[[Config], int]"
Found 2 errors in 1 file (checked 1 source file)

Why would it expect "Callable[[Config], int]"?

I'm using Python-3.8, and mypy==0.800

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葬花如无物 2025-01-23 08:24:10

如果您希望该字段的类型是int的函数或str的函数，您可以

class Config(NamedTuple):
    func: Callable[[int], int] | Callable[[str], int]

这样做这描述了两个函数类型的并集。

然而，这不是一个有用的类型。如果 Python 有交集类型，则这相当于

Callable[[int & str], int]

And int & str 是空类型。不存在同时为 int 和 str 的值。所以这是一类永远不能被调用的函数。并且 isinstance 在这里不会为您提供帮助，因为您无法对 Callable 声明的参数类型进行类型检查。

正如评论中提到的，您可以这样做

Callable[[int | str], int]

，但这是接受 int 或 string 的函数类型，而不是选择性地仅接受两者之一的函数类型。

If you want the type of that field to be either a function of an int or a function of a str, you can do

class Config(NamedTuple):
    func: Callable[[int], int] | Callable[[str], int]

This describes the union of two function types.

However, this is not a useful type. If Python had intersection types, this would be equivalent to

Callable[[int & str], int]

And int & str is, well, the empty type. There are no values which are both int and str at the same time. So this is a type of functions that can never be called. And isinstance won't help you here since you can't typecheck the declared argument types of a Callable.

As mentioned in the comments, you can do