正确向后移植通用集合

发布于 2025-01-15 05:13:20 字数 759 浏览 4 评论 0原文

在 Python 3.9 中，现在可以将 collections.abc 与泛型一起使用，这意味着这样的代码是可能的：

import collections.abc
from typing import TypeVar

T = TypeVar("T")


class MySequence(collections.abc.Sequence[T]):
    ...

但是，在 Python 3.8 中，这是不可能的。相反，必须使用泛型的typing 模块。我想知道解决这个问题的正确方法是什么。现在我正在做以下事情：

import sys
from typing import TypeVar

T = TypeVar("T")

if sys.version_info < (3, 9):
    import collections.abc, typing

    class ABC_Sequence(collections.abc.Sequence, typing.Sequence[T]):
        pass

else:
    from collections.abc import Sequence as ABC_Sequence


class MySequence(ABC_Sequence[T]):
    ...

这是正确的方法吗？

原文

In Python 3.9 it is now possible to use collections.abc with generics, meaning code such as this is possible:

import collections.abc
from typing import TypeVar

T = TypeVar("T")


class MySequence(collections.abc.Sequence[T]):
    ...

In Python 3.8, however, this is not possible. Instead, one must use the typing module for generics. I'm wondering what the proper way to go about this is. Right now I'm doing the following:

import sys
from typing import TypeVar

T = TypeVar("T")

if sys.version_info < (3, 9):
    import collections.abc, typing

    class ABC_Sequence(collections.abc.Sequence, typing.Sequence[T]):
        pass

else:
    from collections.abc import Sequence as ABC_Sequence


class MySequence(ABC_Sequence[T]):
    ...

Is this the proper way to go about it?

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罪#恶を代价 2025-01-22 05:13:20

似乎有些 linter 例如 mypy 不喜欢上面的代码。特别是，mypy 抱怨即使 collections.abc.Sequence 与 typing.Sequence 不同，也使用了重复的基类。看来正确的解决方法是为较低版本实际子类 typing.Sequence 。

import collections.abc
import sys

if sys.version_info < (3, 9):
    from typing import Sequence
else:
    from collections.abc import Sequence


class MySequence(Sequence[T]):
    ...


# For `isinstance` checks at runtime.
if sys.version_info < (3, 9):
    collections.abc.Sequence.register(MySequence)

It seems some linters such as mypy do not like the above code. In particular, mypy complains that duplicate base classes are used even though collections.abc.Sequence is not the same as typing.Sequence. It seems the correct fix is to actually subclass typing.Sequence for lower versions.

import collections.abc
import sys

if sys.version_info < (3, 9):
    from typing import Sequence
else:
    from collections.abc import Sequence


class MySequence(Sequence[T]):
    ...


# For `isinstance` checks at runtime.
if sys.version_info < (3, 9):
    collections.abc.Sequence.register(MySequence)

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