Module 4 Lesson 6: Inheritance: Reusing Code

In programming, we hate repeating ourselves. If you have a SoftwareEngineer class and a Designer class, they both share traits like name, salary, and start_date. Instead of writing that code twice, we can create a "Parent" class and let the other classes Inherit from it.

Lesson Overview

In this lesson, we will cover:

• Parent vs. Child Classes: The hierarchy of code.
• The Syntax for Inheritance: Passing classes inside parentheses.
• The super() Function: Calling the parent's constructor.
• Why use Inheritance?: Organization and time-saving.

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1. Parent and Child Classes

• Parent (Base) Class: The general category (e.g., Animal).
• Child (Derived) Class: The specific type (e.g., Dog or Cat).

The Child class automatically gets all the attributes and methods of the Parent.

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2. Using Inheritance in Python

To inherit, we put the name of the parent class in parentheses when defining the child class.

# The Parent Class
class Animal:
    def __init__(self, name):
        self.name = name

    def eat(self):
        print(f"{self.name} is eating...")

# The Child Class
class Dog(Animal): # Dog inherits from Animal
    def bark(self):
        print("Woof! Woof!")

my_dog = Dog("Buddy")
my_dog.eat() # Buddy is eating... (Method inherited from Animal!)
my_dog.bark() # Woof! Woof! (Specific to Dog)

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3. The super() Function

If your child class needs its own __init__ method (e.g., a Dog needs a breed while other animals don't), you still want to run the parent's __init__ to handle the name. We use super() for this.

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

class Dog(Animal):
    def __init__(self, name, breed):
        # Call the parent's __init__ using super()
        super().__init__(name)
        self.breed = breed

my_dog = Dog("Rex", "German Shepherd")
print(my_dog.name)  # Rex
print(my_dog.breed) # German Shepherd

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4. Why Use Inheritance?

1. DRY (Don't Repeat Yourself): You only write the eat() method once in Animal instead of 100 times for every animal.
2. Organization: It creates a logical structure that models the real world.
3. Extensibility: You can add new behaviors to a Dog without touching the code for Animal.

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Practice Exercise: The Employee System

Create a file named office.py.

1. Define a parent class Employee with name and salary.
2. Add a method show_salary() that prints: "[Name]'s salary is $[Salary]"
3. Define a child class Manager that inherits from Employee.
4. The Manager should also have an attribute department.
5. In the Manager's __init__, use super() to handle the name and salary.
6. Create a manager object and call show_salary().

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Quick Knowledge Check

1. How do you tell Python that a class should inherit from another class?
2. What is the purpose of the super() function?
3. If a parent class has a method run(), does the child class automatically have it?
4. Can a child class have its own attributes that the parent doesn't have?

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Key Takeaways

• Inheritance allows classes to share data and behavior.
• The child class inherits everything from the parent class.
• Use super() to access methods or constructors from the parent class.
• Inheritance reduces code duplication and improves maintenance.

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What’s Next?

Inheritance is great, but what if a child needs to do something differently than its parent? In Lesson 7, we’ll explore Polymorphism and Method Overriding!