Question

当我运行此代码时：

class Node:
    children = []
    num_children = 0
    isleaf = True
    def __init__(self,name):
        print("constructor called for " + name)
        self.name = str(name)



    def add_child(self,child_node):
        print("adding child called "+child_node.name+ " to "+ self.name)
        print("I ("+self.name+ ") have " + str(len(self.children)) + " children")
        print("checking: " + child_node.name + " reports " + str(len(child_node.children)) + " children")
        #cc = copy.deepcopy(child_node)
        self.children.append(child_node)
        #self.children.append(1)
        #self.children[0] = child_node
        print("checking again: " + child_node.name + " reports " + str(len(child_node.children)) + " children")
        self.isleaf = False
        self.num_children = self.num_children +1
        print("I ("+self.name+ ") now have " + str(len(child_node.children)) + " children")



root = Node("a")


testn = Node("b")

root.add_child(testn)


print(root.children[0].name)

我得到了这个输出：

constructor called for a
constructor called for b
adding child called b to a
I (a) have 0 children
checking: b reports 0 children
checking again: b reports 1 children
I (a) now have 1 children
b

为什么代码行：

self.children.append(child_node)

为孩子（B）和父母（A）添加孩子？

我希望它只会将一个孩子添加到父（A）

Answer 1

将children = []移至__init__以使其成为实例成员。现在它是类成员：

def __init__(self, name):
    self.children = []
    self.num_children = 0
    self.isleaf = True

Answer 2

那是因为您将子项定义为类变量而不是实例变量。这意味着children并非真正属于root或testn，而是属于Node类本身。

要解决此问题，只需将children = []替换为self.children = []内的__init__。

将对象追加到列表会修改对象

2 个答案: