Classes and objects in Python - Mini Project: Build & Apply

Classes and Objects

📖 Scenario: You are creating a simple program to manage information about books in a library. Each book has a title and an author.

🎯 Goal: Build a class called Book to represent a book with a title and author. Then create an object of this class and display its details.

📋 What You'll Learn

Create a class named Book with two attributes: title and author.

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

Print the book's title and author using the object's attributes.

💡 Why This Matters

🌍 Real World

Classes help organize data and behavior for real-world things like books, users, or products in software.

💼 Career

Understanding classes and objects is essential for software development jobs, especially in object-oriented programming.

1

Create the Book class

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

Python

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

Hint

Remember, the __init__ method sets up the object's attributes when you create it.

2

Create a Book object

Create an object called 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

# Create the my_book object here
# Your code here

Hint

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

3

Access object attributes

Create two variables: book_title and book_author. Set book_title to my_book.title and book_author to my_book.author.

Python

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

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

# Assign book_title and book_author from my_book
# Your code here

Hint

Use dot notation to get the attributes from the object.

4

Print the book details

Write a print statement to display the text: "Title: {book_title}, Author: {book_author}" using an f-string.

Python

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

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

book_title = my_book.title
book_author = my_book.author

# Print the book details below
# Your code here

Hint

Use an f-string to insert variables inside the string.

Practice

1. What is the main purpose of a class in Python?

easy

A. To execute code immediately

B. To store data in variables only

C. To create a blueprint for objects

D. To perform mathematical calculations

Solution

1. Step 1: Understand what a class represents

   A class is like a blueprint or template that defines how objects are created and what they can do.

2. Step 2: Identify the role of a class

   Classes organize code by grouping data and functions that belong together, allowing creation of many objects from the same blueprint.

3. Final Answer:

   To create a blueprint for objects -> Option C

4. Quick Check:

   Class = blueprint for objects [OK]

Hint: Classes define blueprints; objects are instances [OK]

Common Mistakes:

• Thinking classes run code immediately
• Confusing classes with simple variables
• Believing classes only store data

2. Which of the following is the correct way to define a class named Car in Python?

easy

A. class Car():

B. def Car():

C. function Car():

D. Car class:

Solution

1. Step 1: Recall Python class syntax

   In Python, classes are defined using the keyword class followed by the class name and parentheses.

2. Step 2: Check each option

   class Car(): uses class Car(): which is correct syntax. Others use wrong keywords or formats.

3. Final Answer:

   class Car(): -> Option A

4. Quick Check:

   Class definition starts with 'class' keyword [OK]

Hint: Use 'class ClassName():' to define a class [OK]

Common Mistakes:

• Using 'def' instead of 'class'
• Using 'function' keyword (not Python)
• Missing 'class' keyword

3. What will be the output of this code?

class Dog():
    def __init__(self, name):
        self.name = name
    def bark(self):
        return f"{self.name} says Woof!"

my_dog = Dog("Buddy")
print(my_dog.bark())

medium

A. Error: missing self parameter

B. Buddy says Woof!

C. Dog says Woof!

D. Woof!

Solution

1. Step 1: Understand the __init__ method

   The __init__ method sets the name attribute to "Buddy" when my_dog is created.

2. Step 2: Analyze the bark method call

   The bark method returns a string using the dog's name, so it returns "Buddy says Woof!".

3. Final Answer:

   Buddy says Woof! -> Option B

4. Quick Check:

   Method uses self.name = Buddy [OK]

Hint: Methods use self to access object data [OK]

Common Mistakes:

• Forgetting to pass 'self' in methods
• Confusing class name with object name
• Expecting method to print instead of return

4. Find the error in this class definition:

class Person():
    def __init__(self, name):
        name = name

p = Person("Alice")
print(p.name)

medium

A. Class name should be lowercase

B. Missing self in __init__ parameters

C. print(p.name) should be print(name)

D. Should assign to self.name, not name

Solution

1. Step 1: Check attribute assignment in __init__

   The code assigns name = name, which only changes the local variable, not the object's attribute.

2. Step 2: Correct assignment to object attribute

   It should be self.name = name to store the value in the object for later access.

3. Final Answer:

   Should assign to self.name, not name -> Option D

4. Quick Check:

   Use self.attribute = value to save data [OK]

Hint: Assign attributes with self.attribute = value [OK]

Common Mistakes:

• Assigning to local variable instead of self.attribute
• Forgetting self in method parameters
• Trying to print undefined variables

5. You want to create a class BankAccount that stores an account holder's name and balance. It should have a method deposit(amount) that adds money to the balance only if the amount is positive. Which code correctly implements this?

hard

A. class BankAccount():
def __init__(self, name, balance=0):
self.name = name
self.balance = balance
def deposit(self, amount):
if amount > 0:
self.balance += amount

B. class BankAccount():
def __init__(self, name):
self.name = name
balance = 0
def deposit(self, amount):
self.balance = self.balance + amount

C. class BankAccount():
def __init__(self, name, balance=0):
self.name = name
self.balance = balance
def deposit(self, amount):
self.balance += amount

D. class BankAccount():
def __init__(self, name):
self.name = name
self.balance = 0
def deposit(self, amount):
if amount >= 0:
self.balance = amount

Solution

1. Step 1: Check __init__ method for attributes

   class BankAccount(): def __init__(self, name, balance=0): self.name = name self.balance = balance def deposit(self, amount): if amount > 0: self.balance += amount correctly sets self.name and self.balance with a default balance of 0.

2. Step 2: Verify deposit method logic

   class BankAccount(): def __init__(self, name, balance=0): self.name = name self.balance = balance def deposit(self, amount): if amount > 0: self.balance += amount adds amount to self.balance only if amount > 0, which matches the requirement.

3. Final Answer:

   Correctly implements the class with proper attribute initialization and deposit validation -> Option A

4. Quick Check:

   Check attribute setup and positive amount condition [OK]

Hint: Check attribute setup and validate input in methods [OK]

Common Mistakes:

• Not using self.balance to store balance
• Adding amount without checking if positive
• Overwriting balance instead of adding
• Missing default balance initialization