Class attributes in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of class attribute access

What is the output of this code?

Python

class Dog:
    species = "Canis familiaris"

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

dog1 = Dog("Buddy")
dog2 = Dog("Max")
print(dog1.species)
print(dog2.species)
print(Dog.species)

A Error: species is not defined

B

Canis familiaris
Canis familiaris
Canis familiaris

C

Canis familiaris
Max
Buddy

D

Buddy
Max
Canis familiaris

💡 Hint

Class attributes are shared by all instances unless overridden.

The class attribute 'species' is shared by all instances and the class itself. Accessing it from instances or the class prints the same value.

❓ Predict Output

intermediate

Changing class attribute affects instances

What is the output of this code?

Python

class Car:
    wheels = 4

car1 = Car()
car2 = Car()
Car.wheels = 6
print(car1.wheels)
print(car2.wheels)

A

4
4

B Error: cannot assign to wheels

C

4
6

D

6
6

💡 Hint

Changing a class attribute changes it for all instances that don't override it.

Changing Car.wheels to 6 updates the class attribute. Both car1 and car2 see the updated value because they don't have an instance attribute named wheels.

❓ Predict Output

advanced

Instance attribute shadows class attribute

What is the output of this code?

Python

class Book:
    genre = "Fiction"

b1 = Book()
b2 = Book()
b2.genre = "Non-Fiction"
print(b1.genre)
print(b2.genre)
print(Book.genre)

A

Fiction
Fiction
Fiction

B

Non-Fiction
Non-Fiction
Non-Fiction

C

Fiction
Non-Fiction
Fiction

D Error: genre attribute missing

💡 Hint

Instance attributes override class attributes with the same name.

b2.genre creates an instance attribute that shadows the class attribute. b1.genre and Book.genre remain unchanged.

❓ Predict Output

advanced

Modifying mutable class attribute affects all instances

What is the output of this code?

Python

class Team:
    members = []

team1 = Team()
team2 = Team()
team1.members.append("Alice")
print(team1.members)
print(team2.members)
print(Team.members)

A

['Alice']
['Alice']
['Alice']

B

['Alice']
[]
[]

C

[]
[]
[]

D Error: cannot append to members

💡 Hint

Mutable class attributes are shared by all instances.

The list 'members' is a class attribute shared by all instances. Appending to it via one instance affects all.

🧠 Conceptual

expert

Class attribute behavior with inheritance

Given this code, what is the output?

Python

class Animal:
    sound = "Generic"

class Cat(Animal):
    pass

class Dog(Animal):
    sound = "Bark"

print(Animal.sound)
print(Cat.sound)
print(Dog.sound)

A

Generic
Generic
Bark

B

Generic
Bark
Bark

C

Generic
Generic
Generic

D Error: sound attribute missing in Cat

💡 Hint

Child classes inherit class attributes unless they override them.

Cat inherits 'sound' from Animal, so it prints 'Generic'. Dog overrides 'sound' with 'Bark'.