Python Lesson 21: Inheritance

Inheritance lets a class extend another class, inheriting all its attributes and methods. It models “is-a” relationships and avoids repeating code.

Basic Inheritance

class Animal:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def breathe(self):
        print(f"{self.name} is breathing")
    
    def __str__(self):
        return f"{self.name} (age {self.age})"

# Dog INHERITS from Animal
class Dog(Animal):
    def __init__(self, name, age, breed):
        super().__init__(name, age)  # call parent __init__
        self.breed = breed
    
    def bark(self):
        print(f"{self.name} says: Woof!")

dog = Dog("Rex", 3, "German Shepherd")
dog.breathe()   # inherited from Animal
dog.bark()      # Dog's own method
print(dog)      # uses Animal's __str__

Overriding Methods

class Animal:
    def speak(self):
        print("Some sound...")

class Dog(Animal):
    def speak(self):         # override
        print("Woof!")

class Cat(Animal):
    def speak(self):         # override
        print("Meow!")

class Duck(Animal):
    def speak(self):         # override
        print("Quack!")

animals = [Dog(), Cat(), Duck()]
for animal in animals:
    animal.speak()  # each calls its own version
# Woof!
# Meow!
# Quack!

Real Example: Employee System

class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary
    
    def get_info(self):
        return f"{self.name}: ${self.salary:,}/year"

class Manager(Employee):
    def __init__(self, name, salary, team_size):
        super().__init__(name, salary)
        self.team_size = team_size
    
    def get_info(self):
        base = super().get_info()
        return f"{base} | Team: {self.team_size} people"

class Developer(Employee):
    def __init__(self, name, salary, language):
        super().__init__(name, salary)
        self.language = language
    
    def get_info(self):
        base = super().get_info()
        return f"{base} | Language: {self.language}"

boss = Manager("Alice", 120000, 8)
dev = Developer("Bob", 95000, "Python")
print(boss.get_info())
print(dev.get_info())