AttributeError: 'LinkedList' object has no attribute 'insert_head'

Question

I tried to insert elements in head in a single linkedlist I don't understand what is wrong with my code. it says:

AttributeError: 'LinkedList' object has no attribute 'insert_head'

Here is my code:

class LinkedList:
    def _init_(self):
        # Empty LinkedList
        self.head = None
        # no of nodes in the LinkedList
        self.n = 0

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

    def _len_(self):
        return self.n
    
    def insert_head(self,value):
        #new node
        new_Node = Node(value)

        #Create onnection
        new_Node.next = self.head

        #Reasign head
        self.head = new_Node

        #Increment n
        self.n = self.n + 1

L = LinkedList()

L.insert_head(1)

len(L)

Output should be 5

Answer 1

The reason is pretty obvious, LinkedList has no insert_head method. It's defined in Node class.

In fact Node objects should be a container for data and a reference to the next node, nothing more. They shouldn't be aware of the length of the linked-list for example.

You may refactor your code to something like this:

from __future__ import annotations

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

class LinkedList:
    def __init__(self):
        self.head: Node | None = None
        self.n: int = 0

    def __len__(self):
        return self.n

    def insert_head(self, value):
        new_Node = Node(value)
        new_Node.next = self.head
        self.head = new_Node
        self.n += 1

l = LinkedList()
l.insert_head(20)
print(len(l))  # 1