Python program to insert a new node at the beginning of the Doubly Linked list

When it is required to insert a new node at the beginning of a doubly linked list, a 'Node' class needs to be created. In this class, there are three attributes: the data that is present in the node, the access to the next node of the linked list, and the access to the previous node of the linked list.

Below is a demonstration for the same −

Node Class Structure

First, we define the Node class with three attributes ?

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

Doubly Linked List Implementation

Next, we create the doubly linked list class with methods to add nodes at the beginning and display the list ?

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

class DoublyLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None
    
    def add_data_at_start(self, my_data):
        new_node = Node(my_data)
        if(self.head == None):
            self.head = self.tail = new_node
            self.head.prev = None
            self.tail.next = None
        else:
            new_node.next = self.head
            self.head.prev = new_node
            new_node.prev = None
            self.head = new_node
    
    def print_it(self):
        curr = self.head
        if (self.head == None):
            print("The list is empty")
            return
        print("The nodes in the doubly linked list are :")
        while curr != None:
            print(curr.data)
            curr = curr.next

# Creating instance and adding elements
my_instance = DoublyLinkedList()
print("Elements are being added to the beginning of doubly linked list")

my_instance.add_data_at_start(10)
my_instance.print_it()

my_instance.add_data_at_start(24)
my_instance.print_it()

my_instance.add_data_at_start(54)
my_instance.print_it()

my_instance.add_data_at_start(77)
my_instance.print_it()

my_instance.add_data_at_start(92)
my_instance.print_it()

Output

Elements are being added to the beginning of doubly linked list
The nodes in the doubly linked list are :
10
The nodes in the doubly linked list are :
24
10
The nodes in the doubly linked list are :
54
24
10
The nodes in the doubly linked list are :
77
54
24
10
The nodes in the doubly linked list are :
92
77
54
24
10

How It Works

The insertion process follows these steps:

• Empty List: If the list is empty, the new node becomes both head and tail
• Non-empty List: The new node's next pointer points to the current head, the current head's prev pointer points to the new node, and the new node becomes the new head
• Previous Pointer: The new head's prev pointer is always set to None

Key Components

• The Node class contains data, next, and prev attributes
• The DoublyLinkedList class manages head and tail pointers
• The add_data_at_start method handles insertion at the beginning
• The print_it method displays all nodes from head to tail

Conclusion

Inserting at the beginning of a doubly linked list requires updating both next and prev pointers. The new node becomes the head, and proper linking ensures the bidirectional structure is maintained.