Class attributes in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a class attribute named count initialized to 0.

Python

class MyClass:
    [1] = 0

Drag options to blanks, or click blank then click option'

Aself.count

Bcount

Cdef count

Dinit_count

Attempts:

3 left

💡 Hint

Common Mistakes

Using self.count instead of just count.

Trying to define the attribute inside a method without self.

Using def keyword which is for methods, not attributes.

The class attribute is defined directly inside the class, without self or def. So count = 0 is correct.

2fill in blank

medium

Complete the code to access the class attribute count inside the method show_count.

Python

class MyClass:
    count = 5
    def show_count(self):
        print([1])

Drag options to blanks, or click blank then click option'

Aself.count

Bself.count()

Ccount

DMyClass.count

Attempts:

3 left

💡 Hint

Common Mistakes

Using self.count() which tries to call an attribute as a method.

Using just count which is undefined in method scope.

Using self.count which looks for instance attribute, not class attribute.

To access a class attribute inside a method, use the class name followed by the attribute: MyClass.count.

3fill in blank

hard

Fix the error in the code to correctly increment the class attribute count by 1 inside the method increment.

Python

class MyClass:
    count = 0
    def increment(self):
        MyClass.[1] += 1

Drag options to blanks, or click blank then click option'

Acount

Bself.count

Cincrement

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using self.count which may create an instance attribute instead.

Using wrong capitalization like Count.

Trying to call increment as attribute.

The class attribute count should be accessed with the exact name and class: MyClass.count.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each number to its square, but only for numbers where the class attribute threshold is greater than 5.

Python

class Numbers:
    threshold = 5
    squares = {x: x[1]2 for x in range(1, 6) if x [2] threshold}

Drag options to blanks, or click blank then click option'

A**

B>

C<

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using * instead of ** for power.

Using wrong comparison operator like > instead of <.

Not using the class attribute threshold correctly.

The operator for power is **. The condition should check if x is less than the threshold (5) to include numbers less than 5.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase keys to values, but only include items where the value is greater than 10.

Python

class Data:
    items = {'a': 5, 'b': 15, 'c': 20}
    filtered = [1]: [2] for [3], v in items.items() if v > 10}

Drag options to blanks, or click blank then click option'

Ak.upper()

Bv

Ck

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using items instead of k in the loop.

Not converting keys to uppercase.

Swapping keys and values in the comprehension.

The keys are converted to uppercase with k.upper(), values are v, and the loop variable for keys is k.

Practice

1. What is a class attribute in Python?
class Car:
wheels = 4
Here, what does wheels represent?

easy

A. A value shared by all Car objects

B. A value unique to each Car object

C. A method inside the Car class

D. A variable defined inside a method

Solution

1. Step 1: Identify the attribute location

   The attribute wheels is defined inside the class but outside any method.

2. Step 2: Understand class attribute behavior

   Attributes defined this way are shared by all instances of the class.

3. Final Answer:

   A value shared by all Car objects -> Option A

4. Quick Check:

   Class attribute = shared value [OK]

Hint: Class attributes are outside methods, shared by all instances [OK]

Common Mistakes:

• Thinking class attributes are unique per object
• Confusing class attributes with instance attributes
• Assuming class attributes are methods

2. Which of the following is the correct way to define a class attribute color with value "red" inside a class Fruit?

easy

A. class Fruit:
def __init__(self):
color = "red"

B. class Fruit:
def color(self):
return "red"

C. class Fruit:
def __init__(self, color):
self.color = color

D. class Fruit:
color = "red"

Solution

1. Step 1: Identify class attribute syntax

   A class attribute is defined directly inside the class, outside any method.

2. Step 2: Check each option

   class Fruit: color = "red" correctly defines color as a class attribute. class Fruit: def __init__(self): color = "red" defines a local variable inside __init__. class Fruit: def color(self): return "red" defines a method, not an attribute. class Fruit: def __init__(self, color): self.color = color defines an instance attribute.

3. Final Answer:

   class Fruit: color = "red" -> Option D

4. Quick Check:

   Class attribute = direct assignment inside class [OK]

Hint: Class attributes are assigned directly inside class, outside methods [OK]

Common Mistakes:

• Defining attribute inside __init__ without self
• Confusing methods with attributes
• Using self for class attributes

3. What will be the output of this code?

class Dog:
    species = "Canine"

dog1 = Dog()
dog2 = Dog()
Dog.species = "Wolf"
print(dog1.species)
print(dog2.species)

medium

A. Canine\nCanine

B. Wolf\nCanine

C. Wolf\nWolf

D. Canine\nWolf

Solution

1. Step 1: Understand class attribute change

   The attribute species is a class attribute shared by all instances.

2. Step 2: Effect of changing class attribute

   Changing Dog.species to "Wolf" updates the value for all instances that don't have their own species attribute.

3. Final Answer:

   Wolf\nWolf -> Option C

4. Quick Check:

   Changing class attribute affects all instances [OK]

Hint: Changing class attribute changes it for all instances without override [OK]

Common Mistakes:

• Thinking instances keep old class attribute values
• Confusing instance and class attributes
• Expecting different outputs for dog1 and dog2

4. Find the error in this code snippet:

class Book:
    pages = 100

    def __init__(self, pages):
        pages = pages

b = Book(200)
print(b.pages)

medium

A. The instance attribute pages is not set properly

B. The class attribute pages is overwritten incorrectly

C. Syntax error in __init__ method

D. Cannot print pages attribute directly

Solution

1. Step 1: Analyze __init__ method

   The line pages = pages assigns the parameter to itself, not to the instance.

2. Step 2: Understand instance attribute setting

   To set an instance attribute, it should be self.pages = pages. Without self., the instance attribute is not created.

3. Final Answer:

   The instance attribute pages is not set properly -> Option A

4. Quick Check:

   Use self.pages to set instance attribute [OK]

Hint: Use self.attribute to set instance attributes inside __init__ [OK]

Common Mistakes:

• Forgetting self. when assigning instance attributes
• Assuming parameter assignment sets instance attribute
• Confusing class and instance attributes

5. You want to keep track of how many objects of class Student are created using a class attribute count. Which code correctly updates count each time a new Student is made?

hard

A. class Student:
count = 0
def __init__(self):
self.count += 1

B. class Student:
count = 0
def __init__(self):
Student.count += 1

C. class Student:
def __init__(self):
count = 0
count += 1

D. class Student:
count = 0
def __init__(self):
count += 1

Solution

1. Step 1: Identify class attribute usage

   count is a class attribute, so it should be accessed via the class name inside methods.

2. Step 2: Check each option for correct increment

   class Student: count = 0 def __init__(self): Student.count += 1 uses Student.count += 1, correctly updating the class attribute. class Student: count = 0 def __init__(self): self.count += 1 tries to increment self.count, which creates an instance attribute instead. Options C and D have syntax or scope errors.

3. Final Answer:

   class Student: count = 0 def __init__(self): Student.count += 1 -> Option B

4. Quick Check:

   Update class attribute via ClassName.attribute [OK]

Hint: Use ClassName.attribute to update class attributes inside methods [OK]

Common Mistakes:

• Using self.attribute to update class attribute
• Defining count inside __init__ instead of class
• Forgetting to use class name to access class attribute