Classes & Objects

Overview

Classes are blueprints for creating objects. Objects bundle data variables and functions together.

Learning Objectives

• Define custom classes with init constructors.
• Understand the 'self' parameter in class methods.
• Instantiate objects and access their attributes.

Concept Explanation

A class is a template. The __init__ constructor initializes new object instances. The self parameter references the current object instance, letting you access and modify its variables.

Code Examples

Example 1 — Basics

This example introduces the fundamental syntax and concepts.

class User:
    def __init__(self, name):
        self.name = name

Example 2 — Everyday Usage

This example demonstrates a realistic scenario handling business parameters.

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

    def describe(self):
        return f'{self.title} by {self.author}'

my_book = Book('1984', 'George Orwell')
print(my_book.describe())

Example 3 — Advanced Example

This example shows clean, production-grade code structure following senior development standards.

class BankAccount:
    def __init__(self, owner, balance=0.0):
        self.owner = owner
        self.balance = balance

    def deposit(self, amount):
        if amount <= 0:
            print('Amount must be positive')
            return
        self.balance += amount
        print(f'Deposited {amount}. Balance: {self.balance}')

account = BankAccount('Alex', 100.0)
account.deposit(50.0)

Visual Flow

The following execution flow represents the step-by-step evaluation inside the interpreter:

Declare Class → Call constructor class name → Run __init__ → Bind attributes to self → Return object reference

Common Mistakes

Review these common pitfalls when working with this topic:

• Forgetting to write the 'self' parameter in class method definitions.
• Confusing class-level variables (shared by all instances) with instance variables (unique to each object).
• Invoking class methods without parentheses.
• Using lowercase class names (naming classes using CapitalCamelCase is standard).

Best Practices

Enforce these Pythonic best practices in your codebase:

class employee:
    def setup(emp, n):
        emp.name = n # Missing standard init

class Employee:
    def __init__(self, name):
        self.name = name # Correct initializer

Quick Revision

Use these key summaries for last-minute revision:

• class defines a new blueprint schema.
• init method initializes object attributes.
• self represents the current object instance.
• Methods are functions defined inside classes.
• Access variables using object.attribute.