使用该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

我在下面包含的代码会引发以下错误:

The code I have included below throws the following error:

NameError: name 'Vector2' is not defined 

在这一行:

def Translate (self, pos: Vector2):

为什么 Python 在 Translate 方法中无法识别我的 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(编译类体时)，Vector2还没有定义然而(它当前正在编译，尚未执行名称绑定)；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.

因为这是一个很常见的场景(在类的主体中类型提示一个类)，你应该使用 前向引用，将其括在引号中:

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(以及任何符合 PEP 484 的检查器)将理解您的提示并正确注册.当通过 <访问 __annotations__ 时，Python 确实认识到这一点代码>typing.get_type_hints:

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}

<小时>

这在 Python 3.7 中已经改变；请参阅下面的 abarnert 回答.

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