'NoneType' 对象没有属性 'element'

Question

为什么在下面的代码中，在 while 循环中打印 head.element 时我没有收到任何错误但是循环外的相同代码打印代码让我出错？

class node:
  def __init__(self, element):
        self.element = element
        self.next = None


head = None

node1 = node(1)
node2 = node(2)

head = node1
node1.next = node2

while head != None:
    print(head.element)
    head = head.next

print(head.element)

Answer 1

错误是由您的最后一行代码引发的：

print(head.element)

when/if流到上面那一行，head变量是None，因为while循环只有在head == None时才结束。

while head != None:
    print(head.element)
    head = head.next # The last time this will return None

Answer 2

在上一次 while 循环迭代中，头部为 None，您尝试打印 class None.

的属性元素

'NoneType' 对象没有属性 'element'

'NoneType' object has no attribute 'element'

python

data-structures

linked-list

nonetype