利用python中的单链表实现队列中的AttributeError

我想通过使用单个链表实现一个队列。当我运行下面的代码时,我收到AttributeError。我不知道该怎么解决这个问题。 我假设链表的第一个是队列的前面,第二个是队列的后面。 通过使用while循环,我想连接整个单链表。

class Node:
    def __init__(self, value):
        self.info = value
        self.link = None


class Queue:
    def __init__(self):
        self.front = None


    def enqueue(self, data):
        temp = Node(data)
        p = self.front
        if self.front is None:
            self.front = temp

        while p.link is not None:
            p = p.link
        p.link = temp
        temp.link = None

    def dequeue(self):
        self.front = self.front.link

    def size(self):
        p = self.start
        n = 0
        while p is not None:
            p = p.link
            n += 1
        return n

    def display(self):
        p = self.start
        while p is not None:
            p = p.link
        print(p.info, '', end='')

qu = Queue()

for i in range(4):
    add = int(input("please enter the elements "))
    qu.enqueue(add)
    qu.display()

for i in range(2):
    qu.dequeue()
    qu.display()

Traceback (most recent call last):
  File "C:/Users/HP/Music/Queue_SLList.py", line 43, in <module>
    qu.enqueue(add)
  File "C:/Users/HP/Music/Queue_SLList.py", line 18, in enqueue
    while p.link is not None:
AttributeError: 'NoneType' object has no attribute 'link'