类中的类型提示 [英] type hinting within a class

问题描述

class Node:
    def append_child(self, node: Node):
       if node != None:
        self.first_child = node
    self.child_nodes += [node]

如何做node:Node?因为当我运行它时，它说name 'Node' is not defined.

How do I do node: Node? Because when I run it, it says name 'Node' is not defined.

我是否应该删除 : Node 并在函数内部对其进行实例检查?但是，我如何访问 node 的属性(我希望它是 Node 类的实例)?

Should I just remove the : Node and instance check it inside the function? But then how could I access node's properties (which I would expect to be instance of Node class)?

顺便说一句，我不知道如何在 Python 中实现类型转换.

I don't know how implement type casting in Python, BTW.

推荐答案

self"类型检查中的引用通常使用字符串完成:

"self" references in type checking are typically done using strings:

class Node:
    def append_child(self, node: 'Node'):
       if node != None:
        self.first_child = node
    self.child_nodes += [node]

这在 前向引用" PEP-0484 部分.

This is described in the "Forward references" section of PEP-0484.

请注意，这不会进行任何类型检查或强制转换.这是一个类型提示，python(通常)完全忽略¹.但是，第三方工具(例如 mypy)使用类型提示对您的代码进行静态分析，并可能在运行前生成错误.

Please note that this doesn't do any type-checking or casting. This is a type hint which python (normally) disregards completely¹. However, third party tools (e.g. mypy), use type hints to do static analysis on your code and can generate errors before runtime.

此外，从 python3.7 开始，您可以隐式通过使用from __future__ import annotations(和在python4.0，这将是默认值).

Also, starting with python3.7, you can implicitly convert all of your type-hints to strings within a module by using the from __future__ import annotations (and in python4.0, this will be the default).

^{1提示是内省的——所以如果你真的想的话，你可以使用它们来构建某种使用装饰器等的运行时检查器，但是python默认不会这样做.}

^{1The hints are introspectable -- So you could use them to build some kind of runtime checker using decorators or the like if you really wanted to, but python doesn't do this by default.}

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