OOP principles overview in Python - Mini Project: Build & Apply

OOP Principles Overview

📖 Scenario: Imagine you are creating a simple program to manage a library. You want to organize books and their details using programming concepts that help keep things neat and easy to understand.

🎯 Goal: You will build a small Python program that uses basic Object-Oriented Programming (OOP) principles: creating a class, adding attributes, using a method, and showing how to create and use objects.

📋 What You'll Learn

Create a class named Book

Add attributes title and author to the class

Add a method display_info that prints the book's title and author

Create an object of the Book class with specific title and author

Call the display_info method to show the book details

💡 Why This Matters

🌍 Real World

Organizing data about things like books, movies, or products using classes helps keep programs clear and easy to manage.

💼 Career

Understanding OOP is essential for many programming jobs because it helps build programs that are easier to maintain and expand.

1

Create the Book class with attributes

Create a class called Book with an __init__ method that takes self, title, and author as parameters. Inside __init__, set self.title to title and self.author to author.

Python

# Create the Book class with __init__ method
# Your code here

Hint

Remember, __init__ is a special method to set up new objects. Use self to store the values inside the object.

2

Add the display_info method

Inside the Book class, add a method called display_info that takes only self as a parameter. This method should print the book's title and author in the format: "Title: {self.title}, Author: {self.author}" using an f-string.

Python

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

    # Add display_info method here
    # Your code here

Hint

Use an f-string inside the print statement to show the title and author clearly.

3

Create a Book object

Create an object named my_book from the Book class with the title "The Great Gatsby" and author "F. Scott Fitzgerald".

Python

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

    def display_info(self):
        print(f"Title: {self.title}, Author: {self.author}")

# Create my_book object here
# Your code here

Hint

Use the class name Book followed by parentheses with the title and author as arguments.

4

Call the display_info method

Call the display_info method on the my_book object to print the book's details.

Python

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

    def display_info(self):
        print(f"Title: {self.title}, Author: {self.author}")

my_book = Book("The Great Gatsby", "F. Scott Fitzgerald")

# Call display_info method here
# Your code here

Hint

Use dot notation to call the method: my_book.display_info().

Practice

1. Which of the following is NOT one of the four main principles of Object-Oriented Programming (OOP)?

easy

A. Compilation

B. Inheritance

C. Polymorphism

D. Encapsulation

Solution

1. Step 1: Recall the four main OOP principles

   The four main principles are Encapsulation, Inheritance, Polymorphism, and Abstraction.

2. Step 2: Identify the option not in the list

   Compilation is a process related to converting code, not an OOP principle.

3. Final Answer:

   Compilation -> Option A

4. Quick Check:

   OOP principles exclude Compilation [OK]

Hint: Remember OOP principles: E, I, P, A [OK]

Common Mistakes:

• Confusing compilation with OOP concepts
• Mixing up abstraction with compilation
• Thinking all programming terms are OOP principles

2. Which Python keyword is used to create a new class?

easy

A. def

B. func

C. object

D. class

Solution

1. Step 1: Recall Python syntax for defining classes

   In Python, the keyword class is used to define a new class.

2. Step 2: Check other options

   def defines functions, object is a base class, and func is not a Python keyword.

3. Final Answer:

   class -> Option D

4. Quick Check:

   Use 'class' to define classes [OK]

Hint: Classes start with 'class' keyword in Python [OK]

Common Mistakes:

• Using def instead of class for classes
• Confusing object with class keyword
• Trying to use func which is invalid

3. What will be the output of this code?

class Animal:
    def speak(self):
        return "Sound"

class Dog(Animal):
    def speak(self):
        return "Bark"

pet = Dog()
print(pet.speak())

medium

A. Bark

B. Sound

C. None

D. Error

Solution

1. Step 1: Understand inheritance and method overriding

   Dog class inherits from Animal and overrides the speak method to return "Bark".

2. Step 2: Check which speak method is called

   pet is an instance of Dog, so pet.speak() calls Dog's speak method, returning "Bark".

3. Final Answer:

   Bark -> Option A

4. Quick Check:

   Overridden method returns 'Bark' [OK]

Hint: Child class method overrides parent method [OK]

Common Mistakes:

• Expecting parent class method output
• Confusing method overriding with overloading
• Thinking print outputs None

4. Find the error in this code snippet:

class Car:
    def __init__(self, model):
        self.model = model

    def display(self):
        print(Model)

medium

A. Constructor name is wrong

B. Missing self in display method

C. Model should be self.model in print

D. Class name should be lowercase

Solution

1. Step 1: Check the print statement inside display method

   The print statement uses Model which is undefined; it should use self.model to access the instance variable.

2. Step 2: Verify other parts

   The constructor name __init__ is correct, and method has self parameter. Class name capitalization is fine.

3. Final Answer:

   Model should be self.model in print -> Option C

4. Quick Check:

   Use self to access instance variables [OK]

Hint: Use self.variable to access instance data [OK]

Common Mistakes:

• Forgetting self in method parameters
• Using variable name without self prefix
• Thinking constructor name is incorrect

5. You want to create a class that hides its internal data and only allows access through methods. Which OOP principle does this demonstrate?

hard

A. Inheritance

B. Encapsulation

C. Polymorphism

D. Abstraction

Solution

1. Step 1: Understand the principle of hiding data

   Hiding internal data and controlling access through methods is called Encapsulation.

2. Step 2: Differentiate from other principles

   Inheritance is about reusing code, Polymorphism is about using methods in different ways, Abstraction is about hiding complexity but not necessarily data.

3. Final Answer:

   Encapsulation -> Option B

4. Quick Check:

   Data hiding = Encapsulation [OK]

Hint: Data hiding means Encapsulation [OK]

Common Mistakes:

• Confusing encapsulation with abstraction
• Mixing inheritance with data hiding
• Thinking polymorphism hides data