删除链接列表中间的节点，仅授予对该节点的访问权限。 -Python

Question

I am trying delete the middle node, but when I call the function and try to get hold of second node after the given node, it appears to be None. Below is my code, please help me correct it.

class Node:
    # Constructor to initialize the node object
    def __init__(self, data):
        self.data= data
        self.next= None

class LinkedList():

    # Function to initialize head
    def __init__(self):
        self.head = None

    # Function to insert a new node at the beginning
    def insert(self, data):
        node = Node(data)
        node.next=self.head
        self.head = node

    # Function to print elements of the linked list    
    def printlist(self):
        current = self.head
        while current:
            print current.data 
            current = current.next

    def deleteMiddle(self, node):
        second = node.next
        print second.data
        if node is None:
            return
        node.data = second.data
        node.next = second.next

llist = LinkedList()
llist.insert(10)
llist.insert(15)
mid = Node(20)
llist.insert(mid.data)
llist.insert(16)
llist.insert(17)
llist.insert(19)
print "Before deleting middle or any node"
llist.printlist()
print "After deleting middle or any node"
llist.deleteMiddle(mid)
llist.printlist()

Update 1 : I have added below changes, and it is working fine. But want to know, if it is correct and can be (insert and addNode function) combined into one function. Also I want to understand better way to write this code, as there can be a case, where I want to delete any node and will have access to that node only. With my code, I am defining node and then deleting it, but I still feel there should be better approach than my code.

def addNode(self, node):
        node.next =  self.head
        self.head = node

llist.addNode(mid)

Answer 1

You did not actually insert your mid node into the linked list; instead, you inserted a brand new node into the list with the same data value. Nothing you do via mid will have any effect on your list, as it has no connection to the list.

Answer 2

Right off the bat, it looks like you are adding the data from your middle node mid , rather than the node itself into the head position. When you try to delete mid , you need to find the node in the linked list that looks like mid since it is not the exact same node.

Alternatively, you can choose to add your Node called mid , by creating a new insert function that takes a Node instead of data .

ie, def insert(self, node):