Accessing and modifying attributes in Python - Mini Project: Build & Apply

Accessing and Modifying Attributes

📖 Scenario: You are creating a simple program to manage a book's information. You will work with a Book class that has attributes for the book's title and author.

🎯 Goal: Build a program that creates a Book object, accesses its attributes, modifies one attribute, and then prints the updated information.

📋 What You'll Learn

Create a Book class with title and author attributes

Create an instance of Book with specific title and author

Access and modify the title attribute of the Book instance

Print the updated title and author of the book

💡 Why This Matters

🌍 Real World

Managing and updating information about objects like books, products, or users is common in software applications.

💼 Career

Understanding how to access and modify object attributes is fundamental for programming jobs involving object-oriented programming.

1

Create the Book class and an instance

Create a class called Book with an __init__ method that takes title and author as parameters and assigns them to attributes. Then create an instance called my_book with the title 'The Great Gatsby' and author 'F. Scott Fitzgerald'.

Python

# Create the Book class and the my_book instance
# Your code here

Hint

Define the Book class with an __init__ method that sets self.title and self.author. Then create my_book using the class.

2

Access the title attribute

Create a variable called current_title and set it to the title attribute of the my_book object.

Python

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

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

# Access the title attribute and assign it to current_title
# Your code here

Hint

Use dot notation to get the title from my_book and assign it to current_title.

3

Modify the title attribute

Change the title attribute of my_book to 'The Great Gatsby - Revised Edition'.

Python

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

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

current_title = my_book.title

# Modify the title attribute of my_book
# Your code here

Hint

Use dot notation to assign the new string to my_book.title.

4

Print the updated book information

Print the updated title and author attributes of my_book in the format: Title: [title], Author: [author].

Python

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

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

current_title = my_book.title

my_book.title = 'The Great Gatsby - Revised Edition'

# Print the updated title and author
# Your code here

Hint

Use an f-string to print the updated title and author from my_book.

Practice

1. What is the correct way to access the attribute color of an object car in Python?

easy

A. car.color

B. car[color]

C. car->color

D. car[color()]

Solution

1. Step 1: Understand attribute access syntax

   In Python, attributes of an object are accessed using dot notation: object.attribute.

2. Step 2: Apply to given object and attribute

   For object car and attribute color, the correct syntax is car.color.

3. Final Answer:

   car.color -> Option A

4. Quick Check:

   Dot notation accesses attributes = car.color [OK]

Hint: Use dot (.) to access attributes on objects [OK]

Common Mistakes:

• Using brackets like car[color]
• Using arrow notation like car->color
• Calling attribute as a function like car[color()]

2. Which of the following is the correct syntax to change the attribute age of an object person to 30?

easy

A. person["age"] = 30

B. person.age = 30

C. person->age = 30

D. person.age(30)

Solution

1. Step 1: Recall attribute assignment syntax

   To modify an attribute, use dot notation with assignment: object.attribute = value.

2. Step 2: Apply to given object and attribute

   Set person.age to 30 by writing person.age = 30.

3. Final Answer:

   person.age = 30 -> Option B

4. Quick Check:

   Assign attribute with dot and equals = person.age = 30 [OK]

Hint: Use dot and equals to set attribute: obj.attr = value [OK]

Common Mistakes:

• Using brackets like person["age"] = 30
• Using arrow notation person->age = 30
• Trying to call attribute like a function person.age(30)

3. What will be the output of this code?

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

my_dog = Dog("Buddy")
print(my_dog.name)
my_dog.name = "Max"
print(my_dog.name)

medium

A. Buddy\nBuddy

B. Max\nBuddy

C. Max\nMax

D. Buddy\nMax

Solution

1. Step 1: Understand initial attribute value

   The constructor sets self.name to "Buddy". So, my_dog.name is initially "Buddy".

2. Step 2: Modify attribute and print again

   After printing "Buddy", the code sets my_dog.name = "Max". The second print outputs "Max".

3. Final Answer:

   Buddy Max -> Option D

4. Quick Check:

   Initial then changed attribute prints = Buddy Max [OK]

Hint: Changing attribute updates value printed next [OK]

Common Mistakes:

• Thinking attribute change does not affect output
• Confusing order of prints
• Assuming attribute is immutable

4. Identify the error in this code snippet:

class Cat:
    def __init__(self, color):
        self.color = color

kitty = Cat("black")
print(kitty[color])

medium

A. Using brackets instead of dot to access attribute

B. Missing parentheses in class definition

C. Incorrect constructor name

D. Attribute 'color' not defined

Solution

1. Step 1: Check attribute access syntax

   The code uses kitty[color], which tries to access like a dictionary key, but color is an attribute, not a key.

2. Step 2: Correct syntax for attribute access

   Use dot notation: kitty.color to access the attribute.

3. Final Answer:

   Using brackets instead of dot to access attribute -> Option A

4. Quick Check:

   Attributes use dot, not brackets = Using brackets instead of dot to access attribute [OK]

Hint: Use dot, not brackets, to access attributes [OK]

Common Mistakes:

• Using brackets like kitty[color]
• Thinking attributes are dictionary keys
• Confusing attribute access with indexing

5. Given this class:

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

book1 = Book("1984", "Orwell")
book2 = Book("Animal Farm", "Orwell")

# Change author of book2 to "George Orwell"

Which code correctly updates book2 author without affecting book1?

hard

A. book2["author"] = "George Orwell"

B. Book.author = "George Orwell"

C. book2.author = "George Orwell"

D. book1.author = "George Orwell"

Solution

1. Step 1: Understand instance vs class attributes

   Changing book2.author modifies only that instance's attribute, not book1.

2. Step 2: Avoid changing class attribute or other instance

   Assigning Book.author changes class attribute for all instances; changing book1.author affects wrong object; brackets are invalid syntax.

3. Final Answer:

   book2.author = "George Orwell" -> Option C

4. Quick Check:

   Set instance attribute with dot on correct object = book2.author = "George Orwell" [OK]

Hint: Assign attribute on specific object with dot notation [OK]

Common Mistakes:

• Changing class attribute instead of instance attribute
• Modifying wrong object's attribute
• Using brackets instead of dot notation