Traversal and Printing a Linked List in DSA Python

Mental Model

We move step-by-step through each connected item in the list to see or print its value.

Analogy: Imagine walking down a line of people holding hands, looking at each person's face one by one.

head -> [1] -> [2] -> [3] -> null
          ↑

Dry Run Walkthrough

Input: list: 1 -> 2 -> 3, print all values

Goal: Print all values in the list from start to end in order

Step 1: Start at the head node with value 1

head -> [1 ↑] -> [2] -> [3] -> null

Why: We begin printing from the first node

Step 2: Print value 1 and move to next node

head -> [1] -> [2 ↑] -> [3] -> null

Why: After printing current node, move forward to continue

Step 3: Print value 2 and move to next node

head -> [1] -> [2] -> [3 ↑] -> null

Why: Keep printing each node until we reach the end

Step 4: Print value 3 and move to next node (null)

head -> [1] -> [2] -> [3] -> null ↑

Why: Last node printed, next is null which ends traversal

Result:

1 -> 2 -> 3 -> null

Annotated Code

DSA Python

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

class LinkedList:
    def __init__(self):
        self.head = None

    def append(self, value):
        new_node = Node(value)
        if not self.head:
            self.head = new_node
            return
        curr = self.head
        while curr.next:
            curr = curr.next
        curr.next = new_node

    def print_list(self):
        curr = self.head
        while curr:
            print(curr.value, end=' -> ')
            curr = curr.next
        print('null')

# Driver code
ll = LinkedList()
ll.append(1)
ll.append(2)
ll.append(3)
ll.print_list()

curr = self.head

start traversal from the first node

while curr:

continue until we reach the end (null)

print(curr.value, end=' -> ')

print current node's value followed by arrow

curr = curr.next

move to next node to continue traversal

Output

1 -> 2 -> 3 -> null

Complexity Analysis

Time: O(n) because we visit each of the n nodes exactly once

Space: O(1) because we only use a few variables regardless of list size

vs Alternative: Compared to recursive printing which uses O(n) space on call stack, this iterative approach is more space efficient

Edge Cases

empty list

prints only 'null' since there are no nodes

DSA Python

while curr:

single node list

prints the single value followed by 'null'

DSA Python

while curr:

When to Use This Pattern

When you need to visit or display every item in a linked list, use traversal by moving from head to next until null.

Common Mistakes

Mistake: Forgetting to move to the next node inside the loop, causing an infinite loop
Fix: Add 'curr = curr.next' inside the while loop to advance traversal

Mistake: Printing 'null' inside the loop instead of after traversal ends
Fix: Print 'null' only after the loop finishes to show list end

Summary

It visits each node in the linked list from start to end and prints its value.

Use it when you want to see or process all elements in order in a linked list.

The key is to start at the head and keep moving to the next node until you reach null.