Python循环双链表

Question

我正在创建一个双链接循环列表，但遇到了一些问题。这是我的代码：

#!/usr/bin/env python
class _DoublyLinkedList:
    class _Node(object):
        __slots__ = '_element', '_prev', '_next'
        def __init__(self, element, prev, next):
            self._element = element
            self._prev = prev
            self._next = next
        def getNext(self):
            return self._next
        def __str__(self):
            return str(self._element)
    def __init__(self):
        self._header = self._Node(None, None, None)
        self._trailer = self._Node(None, None, None)
        self._header._next = self._trailer
        self._trailer._prev = self._header
        self._size = 0
    def __len__(self):
        return self._size
    def is_empty(self):
        return self._size == 0
    def _insert_between(self, e, predecessor, successor):
        newest = self._Node(e, predecessor, successor)
        predecessor._next = newest
        successor._prev = newest
        self._size += 1
        return newest
    def _delete_node(self, node):
        predecessor = node._prev
        successor = node._next
        predecessor._next = successor
        successor._prev = predecessor
        self._size -= 1
        element = node._element
        node._prev = node._next = node._element = None
        return element
    def first(self): #return but do not remove the element at front
        if self.is_empty():
            raise Empty("Empty!")
        return self._header._next._element
    def last(self):
        if self.is_empty():
            raise Empty("Empty!")
        return self._trailer._prev._element
    def insert_first(self, e):
        self._insert_between(e, self._header, self._header._next)
    def insert_last(self, e):
        self._insert_between(e, self._trailer._prev, self._trailer)
    def delete_first(self):
        if self.is_empty():
            raise Empty("Empty!")
        return self._delete_node(self._header._next)
    def delete_last(self):
        if self.is_empty():
            raise Empty("Empty!")
        return self._delete_node(self._trailer._prev)
    def __str__(self):
        if self._size == 0:
            return '[]'
        retString = "["
        currentElement = self._header.getNext()
        for i in range(self._size):
            retString += str(currentElement) +", "
            currentElement = self._header.getNext()
        return retString[:-2] + ']'

def main():
    d = _DoublyLinkedList()
    d.insert_first(10)
    print(d.__str__())
    d.insert_last(23)
    d.insert_last(24)
    print(d.__str__())
if __name__ == "__main__":
    main()

对于初学者来说，正如你所看到的，这根本不是循环的，所以任何指针都会有所帮助，但我想弄清楚的是，为什么我的输出是：

[10]
[10, 10, 10]   

这个程序有我试图添加的正确数量的元素，但将它们全部打印为我在前面插入的元素，我不明白为什么。

Answer 1

原因是，每次通过循环，都会得到相同的元素。

currentElement = self._header.getNext()
for i in range(self._size):
    retString += str(currentElement) +", "
    currentElement = self._header.getNext()

将其更改为：

currentElement = self._header.getNext()
for i in range(self._size):
    retString += str(currentElement) +", "
    currentElement = currentElement.getNext()