Understanding Classes

When venturing into the world of programming, especially in data structures and algorithms, one fundamental concept you’ll come across is the use of classes. Classes are the blueprint of objects; they define the properties (attributes) and behaviors (methods) that the objects created from them will have. This concept is crucial in organizing and managing code, especially when dealing with complex data structures like lists, trees, graphs, and more.

What is a Class?

In simple terms, a class is a template for creating objects. Objects are instances of classes. Think of a class as a sketch (prototype) of a house. It contains all the details about the floors, doors, windows, etc. Based on this sketch, you can build as many houses (objects) as you like, each with its own specific characteristics.

Attributes and Methods

  • Attributes: These are the properties or characteristics of a class. For example, if we have a class Dog, attributes could be breed, age, and color.

  • Methods: These are the actions or functions that a class can perform. Continuing with the Dog example, methods could be bark(), eat(), and sleep().

Example: Implementing a Stack

To understand how classes work in practice, let’s implement a simple data structure: a stack. A stack is a linear data structure that follows the Last In, First Out (LIFO) principle. The last element added to the stack will be the first one to be removed.

class Stack:
    def __init__(self):
        self.items = []

    def push(self, item):

    def pop(self):
        if not self.isEmpty():
            return self.items.pop()
            return "Stack is empty."

    def peek(self):
        if not self.isEmpty():
            return self.items[-1]
            return "Stack is empty."

    def isEmpty(self):
        return self.items == []

    def size(self):
        return len(self.items)

How Does This Work?

  1. Initialization: The __init__ method initializes a new instance of the class, creating an empty list items to represent the stack.

  2. Push: The push method adds an item to the top of the stack.

  3. Pop: The pop method removes and returns the top item of the stack. It checks if the stack is empty first to avoid errors.

  4. Peek: The peek method returns the top item of the stack without removing it, allowing us to see what’s at the top without altering the stack.

  5. isEmpty: The isEmpty method checks whether the stack is empty and returns a boolean value.

  6. Size: The size method returns the number of items in the stack.

Usage Example

my_stack = Stack()
print(my_stack.peek())   # Output: B
print(my_stack.size())   # Output: 1

Why Use Classes in Data Structures and Algorithms?

Classes help encapsulate and organize code related to specific data structures or algorithms, making it easier to understand, maintain, and reuse code. For instance, by defining a class for a binary tree, you can easily implement methods to insert, delete, or search for elements without worrying about the underlying data structure every time you want to perform these operations.

Classes also promote the principle of abstraction, allowing you to work with high-level operations without needing to know the details of how these operations are implemented.


Understanding classes and how to use them is crucial in programming, especially when dealing with data structures and algorithms. Classes allow you to encapsulate attributes and methods related to specific data structures, making your code more organized, reusable, and easy to maintain. Start experimenting with classes by implementing simple data structures like stacks or queues, and gradually move on to more complex structures. Happy coding!