1、对一个单链表进行逆序操作。
逆序之前为 head-->A-->B-->C-->None
逆序之后为 head-->C-->B-->A-->None
2、实现

定义节点类
class LNode(object):
    def __init__(self, elem, _next):
        self.elem = elem
        self.next = _next

单链表类
class LinkList(object):
    def __init__(self):
        self.head = None
    
    # 头插法创建单链表
    def prepend(self, elem):
        self.head = LNode(elem, self.head)
    
    # 尾插法创建单聊表
    def append(self, elem):
        # 先判断单链表是否为空
        if self.head is None:
            self.head = LNode(elem, None)
            return 
        p = self.head
        # 需要将指针移动到链表的表尾
        while p.next is not None:
            p = p.next
        p.next = LNode(elem, None)
        
        return 
    
    def reverse_list(self):
        if self.head is None:
            return 
        
        p = self.head
        current = self.head.next
        
        p.next = None

        # 引入第三个指针来逆序链表
        while current is not None:
            temp = current.next
            current.next = p
            p = current
            current = temp
        
        self.head = p  # 最后记得将头指针指向当前头结点的位置
    
    def printall(self):
        p = self.head
        while p:
            print p.elem
            p = p.next
        
if __name__ == '__main__':
    single_list = LinkList()
    for i in range(6):
        single_list.append(i)
    single_list.printall()
     """
    0
    1
    2
    3
    4
    5
     """
    single_list.reverse_list()
    single_list.printall()
    """
    5
    4
    3
    2
    1
    0
    """