Python Linked List Query

Question

Here is the code I am having some issues with:

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

class Solution(object):
    def insert(self, head, data):
        if head == None:
            head = Node(data)
        else:
            current = head
            while current.next:
                current = current.next
            current.next = Node(data)
        return head

    def display(self, head):
        current = head
        while current:
            print(current.data)
            current = current.next

The code itself works fine but I'm having trouble understanding the insert function. Initially,

Head == None

So a new Node is made with argument data, this will be the new head from now on. So if I try to add a new Node to this list, the else is triggered and the new node:

current.next 

is created. So far so good. Now if I wish to add yet another Node, the else condition will trigger again but a new current object is being created, will this not overwrite memory of the old current and thus current.next? How can the program have memory of previous Nodes??

Than you.

Answer 1

不，一个新的当前对象没有被创建，而是变量 current 被重新分配，直到它到达列表中的最后一个元素，然后才创建一个新的 Node 对象并将其分配到列表的末尾。

Answer 2

Current is a local variable that points to a Node object. Overwriting current doesn't destroy the Node, it just makes current point to something else. As long as you have a reference to what current used to point to, you're fine. In this case, because you keep a hold of head , you're always able to work your way through the list.