为什么我的python双向链表中最新的追加没有效果

这是我的双链表deque python代码的一部分.

编写的"appendleft"函数几乎与"append"函数类似，通常是输出.为什么最后一个"append('apple')"代码不能在"Group_of_append"函数中正常输出？

class Node:

    def __init__(self,item,prev,next):

        self.item = item
        self.prev = prev
        self.next = next

class deque:

    def __init__(self,name):

        self.name = name
        self.head = Node(None,None,None)
        self.tail = Node(None,self.head,None)

        self.head.next = self.tail
        self.size = 0

    def append(self,item):
        current = self.head
        new_node = Node(item,None,None)
        while current.next != None:
            current = current.next
        current.next = new_node
        new_node.prev = current
        self.tail = new_node
        self.size += 1
        return
    
    def appendleft(self,item):
        current = self.tail
        new_node = Node(item,None,None)
        while current.prev != None:
            current = current.prev
        current.prev = new_node
        new_node.next = current
        self.head = new_node
        self.size += 1
        return

    def print_list(self): 

        p = self.head

        while p.next != None:
            if p.item == None:
                pass
            else:
                print(p.item,end=' ')
            
            p = p.next

    def Group_of_append(self):
        print('Group_of_append')
        self.append('graphe')
        self.append('cherry')
        self.append('apple')
        self.appendleft('watermelon')
        self.appendleft('strawberry')
        self.print_list()
        print(" ")

deq = deque('name')
deq.Group_of_append()

结果是

strawberry watermelon graphe cherry

_append的组_上的最后一个append代码是self.append('apple')无效.

在定义"append"函数时，我认为由于多了一个大小不够，所以不会有输出.

所以，我改变了deque上的'append'函数，如下所示

    def append(self,item):
        self.size += 1
        current = self.head
        new_node = Node(item,None,None)
        while current.next != None:
            current = current.next
        current.next = new_node
        new_node.prev = current
        self.tail = new_node
        self.size += 1
        return

但结果是一样的(仍然是最新的"append"函数不打印任何内容)

strawberry watermelon graphe cherry