Accessing and modifying attributes in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this attribute access code?

Consider this Python class and code. What will be printed?

Python

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

car = Car('Toyota')
print(car.brand)

A Brand

B car.brand

C Toyota

D Error: attribute not found

💡 Hint

Remember, accessing an attribute with dot notation prints its value.

The attribute 'brand' is set to 'Toyota' in the constructor. Accessing car.brand prints 'Toyota'.

❓ Predict Output

intermediate

What happens when modifying an attribute?

What will be the output after modifying the attribute?

Python

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

p = Person('Alice')
p.name = 'Bob'
print(p.name)

A Bob

B None

C Error: cannot modify attribute

D Alice

💡 Hint

You can change attributes by assigning new values.

The attribute 'name' was changed from 'Alice' to 'Bob'. So printing p.name outputs 'Bob'.

❓ Predict Output

advanced

What is the output when accessing a missing attribute?

What happens when you try to access an attribute that does not exist?

Python

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

d = Dog('Rex')
print(d.age)

A AttributeError

B None

C Rex

D 0

💡 Hint

If an attribute is not set, Python raises an error when accessed.

The attribute 'age' was never set on the object. Accessing it raises AttributeError.

❓ Predict Output

advanced

What is the output after modifying a class attribute?

What will this code print?

Python

class Cat:
    species = 'Felis'

c1 = Cat()
c2 = Cat()
Cat.species = 'Felis catus'
print(c1.species)
print(c2.species)

A Felis\nFelis

B Felis\nFelis catus

C Error: cannot modify class attribute

D Felis catus\nFelis catus

💡 Hint

Class attributes are shared by all instances unless overridden.

Changing Cat.species changes it for all instances. Both print statements output 'Felis catus'.

🧠 Conceptual

expert

Which option causes an error when modifying attributes?

Given this code, which option will cause an error when trying to modify the attribute?

Python

class Immutable:
    __slots__ = ['value']
    def __init__(self, value):
        self.value = value

obj = Immutable(10)

A obj.value = 20

B obj.new_attr = 30

C del obj.value

D print(obj.value)

💡 Hint

Slots restrict adding new attributes not listed.

Because __slots__ limits attributes to 'value', adding 'new_attr' causes AttributeError.

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