If you’re brushing up on data structures in Python, linked lists are a great place to start. Unlike arrays (Python’s built-in lists), linked lists are made up of nodes that point to each other — making them flexible for insertions and deletions.

This post walks you through implementing a basic singly linked list from scratch in Python.

What Is a Linked List?

A linked list is a sequence of nodes where:

  • Each node contains some data.
  • Each node points to the next node.

Think of it as a treasure hunt where each clue leads to the next.

Step 1: Define a Node

class Node:
    def __init__(self, data):
        self.data = data      # Value stored in the node
        self.next = None      # Pointer to the next node

Step 2: Create the LinkedList Class

class LinkedList:
    def __init__(self):
        self.head = None  # Start with an empty list

    def append(self, data):
        # Insert a new node at the end.
        new_node = Node(data)
        if not self.head:
            self.head = new_node
            return

        current = self.head
        while current.next:
            current = current.next
        current.next = new_node

    def prepend(self, data):
        # Insert a new node at the beginning.
        new_node = Node(data)
        new_node.next = self.head
        self.head = new_node

    def delete(self, data):
        # Delete the first node with the given data.
        if not self.head:
            return

        if self.head.data == data:
            self.head = self.head.next
            return

        current = self.head
        while current.next:
            if current.next.data == data:
                current.next = current.next.next
                return
            current = current.next

    def print_list(self):
        # Print all nodes in the list.
        current = self.head
        while current:
            print(current.data, end=" -> ")
            current = current.next
        print("None")

Example Usage

ll = LinkedList()
ll.append(10)
ll.append(20)
ll.append(30)
ll.print_list()  # 10 -> 20 -> 30 -> None

ll.prepend(5)
ll.print_list()  # 5 -> 10 -> 20 -> 30 -> None

ll.delete(20)
ll.print_list()  # 5 -> 10 -> 30 -> None

Why Use Linked Lists?

OperationArray (list)Linked List
Random AccessO(1)O(n)
Insertion/DeletionO(n)O(1)*

*O(1) if you already have a reference to the node

Use linked lists when:

  • You care about insertions/deletions more than fast lookups.
  • You don’t know how many items you’ll need upfront.

Level Up 🧠

Want to go further? Try these challenges:

This is part of my “Data Structures in Python” series. Next up: Stacks & Queues.