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Lesson 11 — OOP & Classes Cheat Sheet

Python

In one line: OOP is a programming paradigm that organises code around objects — bundles of related data (attributes) and behaviour (methods). A class is the blueprint; an instance is the act...

Key Ideas

1What is Object-Oriented Programming?. OOP is a programming paradigm that organises code around objects — bundles of related data (attributes) and behaviour (methods). A class is the blueprint; an instance ...

2Defining a Class. Use the class keyword. The __init__ method (the constructor) runs automatically every time you create an instance. self refers to the instance being created — it must ...

3Dunder Methods — Making Objects Pythonic. Dunder methods (double-underscore methods, also called magic methods) let your objects behave like built-in Python types. Define __str__ to control how an object looks...

4Class Methods & Static Methods. Not all methods need access to a specific instance. Python gives you two decorators: @classmethod for methods that work with the class itself (not an instance), and @s...

5Properties — Controlled Attribute Access. The @property decorator lets you access a method like an attribute. This is Python's way of adding validation or computation to attribute access without breaking the i...

Code Examples

class Student:
    """Represents a student with name, age, and grades."""

    # Class attribute — shared by ALL instances
    school = "BitWithBite Academy"

    def __init__(self, name, age, gpa=0.0):
        # Instance attributes — unique per object
    ...

class ShoppingCart:
    def __init__(self, owner):
        self.owner = owner
        self.items = []

    def add(self, item, price):
        self.items.append((item, price))

    def total(self):
        return sum(p for _, p in self.items)

    # __str__...

class BankAccount:
    _total_accounts = 0    # class attribute — tracked globally
    INTEREST_RATE   = 0.05 # constant — class attribute

    def __init__(self, owner, balance=0):
        self.owner   = owner
        self.balance = balance
        BankAcc...