类内的类型提示[重复]

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

我该怎么做node: Node？因为当我运行它时，它说name 'Node' is not defined.

我应该删除: Node并在函数内部实例检查它？ 但是我怎样才能访问node的属性（我希望它是Node class)?

顺便说一句，我不知道如何在 Python 中实现类型转换。

类型检查中的“self”引用通常使用字符串完成：

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

这在“转发参考文献”PEP-0484 的部分。

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.

另外，从 python3.7 开始，您可以隐含地使用以下命令将所有类型提示转换为模块内的字符串from __future__ import annotations（在 python4.0 中，这将是默认值）。

^{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.}