isinstance 用法

Question

class Node:
    data = None
    next = None

    def __init__(self, data):
        self.data = data

    def add(self, data):
        if self.next is None:
            self.next = Node(data)
        else:
            self.next.add(data)

from com.python.demo1.loki.entity.Node import Node
from com.python.demo1.loki.entity.Student import Student


class NodeUtil:
    root = None
    size = 0

    @classmethod
    def isEmpty(cls):
        if cls.size == 0 or cls.root is None:
            return True
        else:
            return False

    @classmethod
    def add(cls, data):
        if cls.isEmpty():
            cls.root = Node(data)
        else:
            cls.root.add(data)
        cls.size += 1

    @classmethod
    def getSize(cls):
        return cls.size

    @classmethod
    def getRoot(cls):
        return cls.root

    @classmethod
    def toString(cls):
        if cls.isEmpty():
            return ""
        else:
            while cls.root is not None:
                if isinstance(cls.root.data, Student):
                    print(cls.root.data.toString())
                cls.root = cls.root.next

from com.python.demo1.loki.entity.Student import Student
from com.python.demo1.loki.entity.Node import Node
from com.python.demo1.loki.util.NodeUtil import NodeUtil

if __name__ == '__main__':
    for i in range(0, 4):
        stu = Student('loki' + str(i), 22 + i, 80, 174)
        node = Node(stu)
        NodeUtil.add(node)

    print(NodeUtil.getSize())
    NodeUtil.toString()

老师，请问下，当我的Node类中的data是Object类型，我设置了Student的对象进去，为什么在NodeUtil中的toString方法里，用isinstance(cls.root.data, Student)判断，居然是false？我是否还要做什么转换吗？

Answer 1

7七月 2021-06-20 18:28:48

只看这个代码挺难看出问题的，还是先研究下isinstance的常见用法。