用 python实现链表

链表是一种常用的数据结构，可以用 Python 实现。下面是一个简单的链表实现：

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def append(self, data):
        new_node = Node(data)
        if self.head is None:
            self.head = new_node
            return
        last_node = self.head
        while last_node.next:
            last_node = last_node.next
        last_node.next = new_node

    def prepend(self, data):
        new_node = Node(data)
        new_node.next = self.head
        self.head = new_node

    def insert_after_node(self, prev_node, data):
        if not prev_node:
            print("Previous node is not in the list")
            return
        new_node = Node(data)
        new_node.next = prev_node.next
        prev_node.next = new_node

    def delete_node(self, key):
        curr_node = self.head
        if curr_node and curr_node.data == key:
            self.head = curr_node.next
            curr_node = None
            return
        prev_node = None
        while curr_node and curr_node.data != key:
            prev_node = curr_node
            curr_node = curr_node.next
        if curr_node is None:
            return
        prev_node.next = curr_node.next
        curr_node = None

    def print_list(self):
        curr_node = self.head
        while curr_node:
            print(curr_node.data)
            curr_node = curr_node.next

这个链表类包含了 Node 类和 LinkedList 类。Node 类表示链表中的一个节点，包含了数据和指向下一个节点的指针。LinkedList 类包含了链表的头节点 head，以及各种方法来操作链表，如 append、prepend、insert_after_node、delete_node 和 print_list。

下面是一个简单的测试：

llist = LinkedList()
llist.append("A")
llist.append("B")
llist.append("C")
llist.append("D")
llist.prepend("E")
llist.insert_after_node(llist.head.next, "F")
llist.delete_node("B")
llist.print_list()

输出结果：

E
A
F
C
D