支持 __getitem__ 的类的 Python 类型提示 [英] Python type hint for classes that support __getitem__

问题描述

我想向一个函数添加类型提示，该函数将接受带有 __getitem__ 方法的任何对象.例如，在

I want to add type hints to a function that will accept any object with a __getitem__ method. For instance, in

def my_function(hasitems, locator):
    hasitems[locator]

我不想将 hasitems 限制为像 list 或 dict 这样的特定类型.只要它支持 __getitem__，它就是 my_function 的合适参数.如何在没有不必要限制的情况下注释其类型?

I don't want to restrict hasitems to be a specific type like list or dict. As long as it supports __getitem__, it's an appropriate argument to my_function. How can I annotate its type without being unnecessarily restrictive?

显然 PyCharm 可以在许多常见情况下推断出适当的提示，但在我的实际用例中却不能.我无法发布代码，因为它用于工作，而且我无法找到 PyCharm 失败的非专有最小示例.在任何情况下，原始问题都没有引用 PyCharm，它仍然是类型提示的有效用例.

apparently PyCharm can deduce the appropriate hint in a number of common cases, but not in my actual use case. I can't post the code since it's for work, and I haven't been able to find a nonproprietary minimal example where PyCharm fails. In any case, the original question doesn't reference PyCharm and it is still a valid use case for type hints.

推荐答案

如果您愿意为 typing 安装一个不太正式的扩展，typing-extensions，你可以使用Protocol，它应该是PEP-0544:

If you're willing to install a not-quite-offical extension to typing, typing-extensions, you can use a Protocol, which should be an implementation of PEP-0544:

from typing_extensions import Protocol
from typing import Any

class GetItem(Protocol):
    def __getitem__(self: 'Getitem', key: Any) -> Any: pass

class BadGetItem:
    def __getitem__(self, a: int, b: int) -> Any: pass

def do_thing(arg: GetItem):
    pass

do_thing(dict())  # OK
do_thing(BadGetItem())  # Fails with explanation of correct signature
do_thing(1)  # Fails

这篇关于支持 __getitem__ 的类的 Python 类型提示的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！