使用类作为其方法中参数的类型提示 [英] Using the class as a type hint for arguments in its methods

问题描述

我下面包含的代码引发以下错误:

The code I have included below throws the following error:

NameError: name 'Vector2' is not defined 

在此行:

def Translate (self, pos: Vector2):

为什么Python无法在Translate方法中识别我的Vector2类?

Why does Python not recognize my Vector2 class in the Translate method?

class Vector2:

    def __init__(self, x: float, y: float):

        self.x = x
        self.y = y

    def Translate(self, pos: Vector2):

        self.x += pos.x
        self.y += pos.y

推荐答案

因为遇到Translate(在编译类主体时)，所以尚未定义Vector2(当前正在编译，名称绑定还没有尚未执行)； Python自然会抱怨.

Because when it encounters Translate (while compiling the class body), Vector2 hasn't been defined yet (it is currently compiling, name binding hasn't been performed); Python naturally complains.

由于这是一种常见的情况(在该类的主体中键入类的提示)，因此应使用

Since this is such a common scenario (type-hinting a class in the body of that class), you should use a forward reference to it by enclosing it in quotes:

class Vector2:    
    # __init__ as defined

    def Translate(self, pos: 'Vector2'):    
        self.x += pos.x
        self.y += pos.y

Python(以及所有符合PEP 484的检查器)将理解您的提示并进行适当的注册.通过 typing.get_type_hints 访问__annotations__时，Python会识别出此错误>:

Python (and any checkers complying to PEP 484) will understand your hint and register it appropriately. Python does recognize this when __annotations__ are accessed through typing.get_type_hints:

from typing import get_type_hints

get_type_hints(Vector2(1,2).Translate)
{'pos': __main__.Vector2}

---

此功能自Python 3.7起已更改；请参阅下面的 abarnert的答案.

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