Python - Inheritance

Overview

Estimated time: 25–35 minutes

Use inheritance to reuse behavior and specialize subclasses. Learn when to prefer composition.

Learning Objectives

• Define base and derived classes; override methods.
• Use super() to delegate to parent implementations.
• Choose composition over inheritance when appropriate.

Prerequisites

• Python - OOP Basics

Basic inheritance

class Shape:
    def area(self) -> float:
        return 0.0

class Rectangle(Shape):
    def __init__(self, w: float, h: float):
        self.w = w; self.h = h
    def area(self) -> float:
        return self.w * self.h

print(Rectangle(3, 4).area())

Using super()

class Logger:
    def log(self, msg: str) -> None:
        print(f"LOG: {msg}")

class TimestampLogger(Logger):
    def log(self, msg: str) -> None:
        from datetime import datetime
        super().log(f"{datetime.now().isoformat()} - {msg}")

TimestampLogger().log("hello")

Composition over inheritance

class Service:
    def __init__(self, logger: Logger):
        self.logger = logger
    def run(self):
        self.logger.log("running")

Service(TimestampLogger()).run()

Common Pitfalls

• Deep inheritance hierarchies; prefer shallow trees and clear responsibilities.
• Forgetting to call super().__init__ in cooperative multiple inheritance.

Checks for Understanding

1. What does super() do?
2. When might composition be a better fit than inheritance?

Exercises

1. Create an Employee base class and a Manager subclass that overrides a method.
2. Refactor an inheritance use into composition and compare readability.