Lesson 49: Inheritance - Python Course

Introduction to Inheritance

Inheritance allows a class to inherit attributes and methods from another class. The class that inherits is called a child class (or subclass), and the class being inherited from is called a parent class (or superclass).

Inheritance promotes code reuse and helps model "is-a" relationships. For example, a Dog is an Animal, so Dog can inherit from Animal.

Basic Inheritance

To create a child class, put the parent class name in parentheses after the class name:

inheritance.py
# Parent class
class Animal:
    def __init__(self, name):
        self.name = name
    
    def speak(self):
        print(f"{self.name} makes a sound")

# Child class
class Dog(Animal):
    def speak(self):
        print(f"{self.name} barks")

class Cat(Animal):
    def speak(self):
        print(f"{self.name} meows")

# Create objects
dog = Dog("Buddy")
cat = Cat("Whiskers")

dog.speak()  # Buddy barks
cat.speak()  # Whiskers meows

Overriding Methods

Child classes can override parent methods by defining a method with the same name:

overriding.py
class Shape:
    def area(self):
        return 0

class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height
    
    def area(self):
        # Override parent method
        return self.width * self.height

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius
    
    def area(self):
        # Override parent method
        return 3.14159 * self.radius ** 2

rect = Rectangle(5, 3)
print(rect.area())  # 15

circle = Circle(4)
print(circle.area())  # 50.27

Using super()

The super() function allows you to call parent class methods from a child class:

super_function.py
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def introduce(self):
        print(f"I'm {self.name}, {self.age} years old")

class Student(Person):
    def __init__(self, name, age, student_id):
        super().__init__(name, age)  # Call parent __init__
        self.student_id = student_id
    
    def introduce(self):
        super().introduce()  # Call parent method
        print(f"My student ID is {self.student_id}")

student = Student("Alice", 20, "S123")
student.introduce()

Best Practices

✅ Inheritance Tips

• Use inheritance for "is-a" relationships

• Override methods to provide specific behavior

• Use super() to call parent methods

• Don't overuse inheritance - composition is sometimes better

• Keep inheritance hierarchies shallow