(任何)类的 Python 类型提示 [英] Python type hint for (any) class

问题描述

我想输入提示以下函数:

I want to type hint the following function:

def get_obj_class(self) -> *class*:
  return self.o.__class__

self.o 可以是任何类型，在运行时确定.

self.o could be of any type, it's determined at runtime.

*class* 显然不是这里的答案，因为它是无效的语法.但是正确答案是什么?我找不到任何关于此的文档，感谢您的帮助.

*class* obviously is not the answer here, because it's invalid syntax. But what is the right answer? I could not find any documentation on this, any help is appreciated.

同样，如果我有一个返回 cls 实例的函数 f(cls: *class*)，有没有办法输入提示适当地返回值?

On a similar note, if I have a function f(cls: *class*) which returns an instance of cls, is there a way to type hint the return value appropriately?

推荐答案

我建议结合使用 TypeVar，表示您的 self.o 值可以是任意类型，Type，方法如下:

I'd recommend using a combination of TypeVar, to indicate that your self.o value could be any arbitrary type, and Type, in the following way:

from typing import TypeVar, Type

T = TypeVar('T')

class MyObj:
    def __init__(self, o: T) -> None:
        self.o = o

    def get_obj_class(self) -> Type[T]:
        return type(self.o)

def accept_int_class(x: Type[int]) -> None:
    pass

i = MyObj(3)
foo = i.get_obj_class()
accept_int_class(foo)    # Passes

s = MyObj("foo")
bar = s.get_obj_class()
accept_int_class(bar)    # Fails

如果你想让 o 的类型更加动态，你可以显式或隐式地给它一个 Any 类型.

If you want the type of o to be even more dynamic, you could explicitly or implicitly give it a type of Any.

关于你的后一个问题，你会这样做:

Regarding your latter question, you'd do:

def f(cls: Type[T]) -> T:
    return cls()

请注意，在实例化类时需要小心——我不记得 Pycharm 在这里做了什么，但我知道 mypy 目前不会检查以确保您正在调用 __init__ 正确运行/使用正确数量的参数.

Note that you need to be careful when instantiating your class -- I don't remember what Pycharm does here, but I do know that mypy currently does not check to make sure you're calling your __init__ function correctly/with the right number of params.

(这是因为 T 可以是任何东西，但无法暗示构造函数应该是什么样子，因此执行此检查最终要么不可能，要么非常困难.)

(This is because T could be anything, but there's no way to hint what the constructor ought to look like, so performing this check would end up being either impossibly or highly difficult.)

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