What is the difference between an array and a linked list in Python?

Question

Jayant Kumar · Accepted Answer

Table of Contents
Introduction
In Python, both arrays and linked lists are fundamental data structures, but they differ in structure, memory usage, and performance. Understanding these differences can help you choose the appropriate data structure for specific use cases in your Python programs.
1. Structure and Memory Layout
Array
An array is a collection of elements stored in contiguous memory locations. In Python, arrays are implemented using the list or array module. This structure allows quick access to elements via indexing, as all elements are stored together.

Advantages:
Arrays offer constant time O(1) access to elements because of their fixed-size, contiguous memory allocation.
Disadvantages:
Inserting or deleting elements in the middle of an array can be costly (O(n)) because all subsequent elements need to be shifted.

Linked List
A linked list consists of nodes where each node holds a reference (or pointer) to the next node. Linked lists can be singly linked or doubly linked (where each node also has a reference to the previous node).

Advantages:
Linked lists excel in dynamic memory allocation and allow for efficient O(1) insertions or deletions at any position, as no elements need to be shifted.
Disadvantages:
Access to linked list elements requires traversal from the head node (O(n)), making random access less efficient.

2. Performance and Use Cases
Performance

Array: Arrays offer better performance for read operations, especially when frequent access to elements via index is required. They also work well in scenarios where the size of the dataset is relatively fixed.
Linked List: Linked lists perform better when frequent insertions or deletions are needed, especially in scenarios where the size of the dataset may vary significantly.

Use Cases

Array: Useful when random access is needed, such as when working with collections where elements are accessed by their index (e.g., sorting algorithms, lookups).
Linked List: Ideal for implementing dynamic data structures like stacks, queues, or when the dataset size fluctuates frequently, and frequent insertions or deletions are necessary.

Practical Examples

Array Example in Python:
# Using a Python list (array-like structure)
array = [1, 2, 3, 4, 5]
print(array[2])  # Accessing element at index 2
array.append(6)  # Adding an element
array.remove(3)  # Removing an element

Linked List Example in Python:
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

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

def append(self, data):
        new_node = Node(data)
        if self.head is None:
            self.head = new_node
        else:
            current = self.head
            while current.next:
                current = current.next
            current.next = new_node

# Create a linked list
ll = LinkedList()
ll.append(1)
ll.append(2)
ll.append(3)

Conclusion
Arrays and linked lists serve different purposes in Python. Arrays are best for scenarios requiring quick access to elements, while linked lists are optimal for dynamic memory management with frequent insertions and deletions. By understanding their structural and performance differences, you can select the right data structure for your Python applications.

What is the difference between an array and a linked list in Python?

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