python实现双向链表

废话不多说，直接贴代码（python 3.6.7)：

#-*-coding=utf-8-*-
class Node(object):
    """结点"""
    def __init__(self,item):
        self.elem=item
        self.next=None
        self.prev=None

class DoubleLinkList(object):
    """双链表"""
    def __init__(self,node=None):
        self.__head = node

    def is_empty(self):
        """判断是否为空"""
        return self.__head==None

    def length(self):
        """链表长度"""
        #cur游标，用来移动遍历节点
        cur = self.__head
        #count记录数量
        count=0
        while cur!=None:
            cur=cur.next
            count+=1
        return count

    def travel(self):
        """遍历整个链表"""
        cur=self.__head
        while cur!=None:
            print(cur.elem)
            cur=cur.next

    def add(self,item):
        """链表头部添加元素"""
        node=Node(item)
        node.next=self.__head
        self.__head=node
        node.next.prev=node

    def append(self,item):
        """链表尾部添加元素"""
        node=Node(item)
        if self.is_empty():
            self.__head=node
        else:
            cur=self.__head
            while cur.next!=None:
                cur=cur.next
            cur.next=node
            node.prev=cur

    def insert(self,pos,item):
        """指定位置添加元素"""
        if pos<=0:
            self.add(item)
        elif pos>self.length()-1:
            self.append(item)
        else:
            cur=self.__head
            count=0
            while count<pos:
                count+=1
                cur=cur.next
            node=Node(item)
            node.next=cur
            node.prev=cur.prev
            cur.prev.next=node
            cur.prev=node


    def remove(self,item):
        """删除节点"""
        cur=self.__head

        while cur!=None:
            if cur.elem==item:
                if cur==self.__head:
                    self.__head=cur.next
                    if cur.next:
                        cur.next.prev=None
                else:
                    cur.prev.next=cur.next
                    cur.next.prev=cur.prev
                break
            else:
                cur=cur.next


    def search(self,item):
        """查找节点是否存在"""
        cur=self.__head
        while cur!=None:
            if cur.elem==item:
                return True
            else:
                cur.next
        return False

if __name__=="__main__":
     dll=DoubleLinkList()
     print(dll.is_empty())
     print(dll.length())
     dll.append(1)
     print(dll.is_empty())
     print(dll.length())
     dll.append(2)
     dll.add(8)
     dll.append(3)
     dll.append(4)
     dll.append(5)
     dll.append(6)
     dll.append(7)
     dll.append(8)
     dll.travel()
     dll.insert(3,100)
     dll.travel()
     dll.remove(8)
     dll.travel()
     dll.travel()
     dll.remove(100)
     dll.insert(100,200)
     dll.travel()