What Is a Linked List?

A chain of nodes

A linked list stores items in separate little boxes called nodes. Each node holds a value and a link (pointer) to the next node. The first node is the head; the last node points to None.

Think of it like this: A treasure hunt: each clue tells you where the next clue is hidden. You can't jump to clue 5 – you have to follow clues 1, 2, 3 and 4 to get there.

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

# build  10 -> 20 -> 30
head = Node(10)
head.next = Node(20)
head.next.next = Node(30)

current = head
while current is not None:        # walk the chain
    print(current.value)
    current = current.next

Output

10
20
30

Building from a Python list

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

def build(values):
    head = None
    for v in reversed(values):       # add to the front, from the last value back
        node = Node(v)
        node.next = head
        head = node
    return head

def show(head):
    parts = []
    while head:
        parts.append(str(head.value))
        head = head.next
    return " -> ".join(parts) + " -> None"

print(show(build([3, 1, 4, 1, 5])))

Output

3 -> 1 -> 4 -> 1 -> 5 -> None

Array vs linked list

Remember: Linked lists are great when you add and remove at the front a lot, and bad when you need to jump to position i.