Method overriding in Python - Mini Project: Build & Apply

Method overriding

📖 Scenario: Imagine you are creating a simple program for a zoo. You want to describe animals and how they make sounds. Different animals make different sounds, but they all share the idea of making a sound.

🎯 Goal: You will build two classes: a base class Animal with a method make_sound, and a derived class Dog that overrides the make_sound method to show a different sound.

📋 What You'll Learn

Create a class called Animal with a method make_sound that prints 'Some generic sound'.

Create a class called Dog that inherits from Animal.

Override the make_sound method in Dog to print 'Bark!'.

Create an object of Animal and call its make_sound method.

Create an object of Dog and call its make_sound method.

💡 Why This Matters

🌍 Real World

Method overriding is used in many programs where different objects share common behavior but need to customize it. For example, different animals making different sounds in a zoo app.

💼 Career

Understanding method overriding is essential for object-oriented programming, which is widely used in software development jobs to create flexible and reusable code.

1

Create the base class Animal

Create a class called Animal with a method make_sound that prints 'Some generic sound'.

Python

# Your code here

Hint

Use class Animal: to start the class. Define make_sound with def make_sound(self): and inside it use print('Some generic sound').

2

Create the Dog class inheriting Animal

Create a class called Dog that inherits from Animal.

Python

class Animal:
    def make_sound(self):
        print('Some generic sound')

# Your code here

Hint

Use class Dog(Animal): to create the Dog class that inherits from Animal. For now, use pass inside.

3

Override the make_sound method in Dog

Override the make_sound method in the Dog class to print 'Bark!'.

Python

class Animal:
    def make_sound(self):
        print('Some generic sound')

class Dog(Animal):
    # Your code here

Hint

Inside Dog, define def make_sound(self): and inside it use print('Bark!').

4

Create objects and call make_sound

Create an object called animal of class Animal and call its make_sound method. Then create an object called dog of class Dog and call its make_sound method.

Python

class Animal:
    def make_sound(self):
        print('Some generic sound')

class Dog(Animal):
    def make_sound(self):
        print('Bark!')

# Your code here

Hint

Create animal = Animal() and call animal.make_sound(). Then create dog = Dog() and call dog.make_sound().

Practice

1.

What is method overriding in Python?

Choose the best description.

easy

A. A child class provides a new version of a method from its parent class.

B. A method that is called automatically when an object is created.

C. A method that cannot be changed once defined in a class.

D. A method that is only accessible inside the class it is defined.

Solution

1. Step 1: Understand method overriding concept

   Method overriding means a child class changes a method from its parent by defining a method with the same name.

2. Step 2: Match description to concept

   A child class provides a new version of a method from its parent class. correctly describes this behavior, while others describe different concepts.

3. Final Answer:

   A child class provides a new version of a method from its parent class. -> Option A

4. Quick Check:

   Method overriding = child changes parent method [OK]

Hint: Child class method with same name replaces parent method [OK]

Common Mistakes:

• Confusing overriding with overloading
• Thinking overriding means creating a new method
• Believing methods cannot be changed in child classes

2.

Which of the following is the correct way to override a method greet in a child class?

class Parent:
    def greet(self):
        print("Hello from Parent")

class Child(Parent):
    # What goes here?

easy

A. def greet():
print("Hello from Child")

B. def greet(self):
print("Hello from Child")

C. def greet(self, name):
print(f"Hello {name} from Child")

D. def greet(self):
return "Hello from Child"

Solution

1. Step 1: Check method signature for overriding

   The child method must have the same name and parameters as the parent method to override it properly.

2. Step 2: Compare options

   def greet(self): print("Hello from Child") matches the parent's method signature exactly. def greet(): print("Hello from Child") misses 'self', C adds a parameter, and D returns a string instead of printing.

3. Final Answer:

   def greet(self):\n print("Hello from Child") -> Option B

4. Quick Check:

   Same method name and parameters = correct override [OK]

Hint: Match method name and parameters exactly to override [OK]

Common Mistakes:

• Omitting 'self' parameter in method
• Changing method parameters when overriding
• Returning value instead of matching parent's behavior

3.

What will be the output of the following code?

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

class Dog(Animal):
    def sound(self):
        print("Bark")

pet = Dog()
pet.sound()

medium

A. Some sound

B. None

C. Error: Method not found

D. Bark

Solution

1. Step 1: Identify method overriding in Dog class

   Dog class overrides the sound() method from Animal to print "Bark" instead of "Some sound".

2. Step 2: Check which method is called

   When pet.sound() is called, it uses Dog's version, printing "Bark".

3. Final Answer:

   Bark -> Option D

4. Quick Check:

   Child method called = overridden output [OK]

Hint: Child method replaces parent method output [OK]

Common Mistakes:

• Expecting parent method output instead of child's
• Thinking method call causes error
• Confusing print output with return value

4.

Find the error in this code that tries to override a method:

class Vehicle:
    def start(self):
        print("Vehicle started")

class Car(Vehicle):
    def start():
        print("Car started")

c = Car()
c.start()

medium

A. Missing 'self' parameter in Car's start method

B. Car class should not inherit Vehicle

C. Parent method start() is private and cannot be overridden

D. Calling start() without parentheses

Solution

1. Step 1: Check method signature in child class

   Car's start method is missing the 'self' parameter, which is required for instance methods.

2. Step 2: Understand impact of missing 'self'

   Without 'self', Python treats start as a static method, causing a TypeError when called on an instance.

3. Final Answer:

   Missing 'self' parameter in Car's start method -> Option A

4. Quick Check:

   Instance methods need 'self' parameter [OK]

Hint: Always include 'self' as first parameter in instance methods [OK]

Common Mistakes:

• Forgetting 'self' in child method
• Thinking inheritance causes error
• Misunderstanding method call syntax

5.

Given the classes below, what will be the output when c.describe() is called?

class Parent:
    def describe(self):
        print("Parent description")

class Child(Parent):
    def describe(self):
        print("Child description")
        super().describe()

c = Child()
c.describe()

hard

A. Child description

B. Parent description\nChild description

C. Child description\nParent description

D. Error: super() used incorrectly

Solution

1. Step 1: Understand method overriding with super()

   Child's describe() overrides Parent's but calls super().describe() to run parent's method too.

2. Step 2: Trace method calls

   Calling c.describe() prints "Child description" first, then calls Parent's describe() printing "Parent description".

3. Final Answer:

   Child description\nParent description -> Option C

4. Quick Check:

   super() calls parent method after child override [OK]

Hint: super() calls parent method inside child override [OK]

Common Mistakes:

• Expecting only child's print output
• Thinking super() causes error
• Confusing order of prints