Python class 属性不能使用它自己的对象

Question

我是 python 的新手，正在编写两个 classes 来定义单链表对象。我的 _Node class 有问题。对于 _Node class 的 'next' 属性，我想将其类型设置为 _Node 对象或 None，这就是我写 Optional[_Node] 的地方。但是 Pycharm IDE 不识别它。有人可以帮我解决这个问题吗？非常感谢。

from typing import Any, Optional

class _Node:
    """ A node in a linked list.

    Note that this is considered a "private class", one which is only meant
    to be used in this module by the LinkedList class, but not by client 
    code.

    === Attributes ===
    item:
        The data stored in this node.
    next:
        The next node in the List, or None if there are no more nodes.
    """

    item: Any
    next: Optional[_Node]

    def __init__(self, item: Any):
        """ Initialize a new node storing <item>, with no next node.
        """
        self.item = item
        self.next = None # Initailly pointing to nothing

Answer 1

您需要在文件顶部进行以下导入，以启用对具有 not yet been defined

的类的引用

from __future__ import annotations

Python class 属性不能使用它自己的对象

Python class attribute can't use its own object

python

attributes

class

nodes

singly-linked-list