Modifying object state in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to change the attribute 'color' of the car object to 'red'.

Python

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

car = Car('blue')
car.color = [1]
print(car.color)

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

A'green'

B'blue'

C'yellow'

D'red'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the color name.

Trying to assign to the class instead of the object.

Assigning 'red' to car.color changes the car's color to red.

2fill in blank

medium

Complete the method to update the 'speed' attribute of the Bike object.

Python

class Bike:
    def __init__(self, speed):
        self.speed = speed
    def set_speed(self, new_speed):
        self.speed = [1]

bike = Bike(10)
bike.set_speed(20)
print(bike.speed)

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

A20

Bnew_speed

Cself.speed

Dspeed

Attempts:

3 left

💡 Hint

Common Mistakes

Using the attribute name instead of the parameter.

Assigning a fixed number instead of the parameter.

The method parameter new_speed holds the new value to assign to self.speed.

3fill in blank

hard

Fix the error in the method that increases the 'count' attribute by 1.

Python

class Counter:
    def __init__(self):
        self.count = 0
    def increment(self):
        self.count [1] 1

counter = Counter()
counter.increment()
print(counter.count)

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

A-=

B=

C+=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which replaces the value instead of adding.

Using '-=' or '*=' which change the value incorrectly.

The += operator adds 1 to the current value of self.count.

4fill in blank

hard

Fill both blanks to create a method that doubles the 'value' attribute of the object.

Python

class Number:
    def __init__(self, value):
        self.value = value
    def double(self):
        self.value = self.value [1] [2]

num = Number(5)
num.double()
print(num.value)

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

A*

B+

C2

Dself.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication.

Using the wrong number or variable.

Multiplying self.value by 2 doubles its value.

5fill in blank

hard

Fill all three blanks to create a method that resets the 'score' attribute to zero and returns it.

Python

class Game:
    def __init__(self):
        self.score = 10
    def reset_score(self):
        self.score = [1]
        return [2]

player = Game()
result = player.reset_score()
print([3])

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

A0

Bself.score

Cresult

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Returning or printing the wrong variable.

Not resetting the attribute to zero.

The method sets self.score to 0, returns it, and the returned value is stored in result which is printed.

Practice

1. What does it mean to modify the state of an object in Python?

easy

A. Changing the values of its attributes

B. Creating a new object

C. Deleting the object

D. Printing the object

Solution

1. Step 1: Understand object state

   The state of an object is stored in its attributes (variables inside the object).

2. Step 2: What modifying state means

   Modifying state means changing these attribute values to new ones.

3. Final Answer:

   Changing the values of its attributes -> Option A

4. Quick Check:

   Modify state = change attribute values [OK]

Hint: State means attribute values; changing them modifies state [OK]

Common Mistakes:

• Confusing creating a new object with modifying state
• Thinking printing changes state
• Mixing deleting object with modifying state

2. Which of the following is the correct way to change an object's attribute color to 'blue'?

easy

A. object.color('blue')

B. object->color = 'blue'

C. object.color = 'blue'

D. object[color] = 'blue'

Solution

1. Step 1: Attribute assignment syntax

   In Python, to change an attribute, use dot notation: object.attribute = value.

2. Step 2: Check each option

   object.color = 'blue' uses correct dot notation. Options A, B, and C use invalid syntax for attribute assignment.

3. Final Answer:

   object.color = 'blue' -> Option C

4. Quick Check:

   Use dot and = to assign attribute [OK]

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

Common Mistakes:

• Using brackets [] instead of dot for attributes
• Using arrow -> which is not Python syntax
• Trying to call attribute like a function

3. What will be the output of this code?

class Box:
    def __init__(self):
        self.size = 5

    def enlarge(self):
        self.size += 3

b = Box()
b.enlarge()
print(b.size)

medium

A. 5

B. 8

C. 3

D. Error

Solution

1. Step 1: Initial attribute value

   The Box object b starts with size = 5 from __init__.

2. Step 2: Method enlarge changes size

   Calling b.enlarge() adds 3 to size, so size becomes 5 + 3 = 8.

3. Final Answer:

   8 -> Option B

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Add changes inside method to attribute value [OK]

Common Mistakes:

• Forgetting method changes attribute
• Thinking size resets after method call
• Expecting error due to method call

4. Find the error in this code that tries to update an object's attribute:

class Car:
    def __init__(self):
        self.speed = 0

    def accelerate(self):
        speed += 10

c = Car()
c.accelerate()
print(c.speed)

medium

A. Using speed without self inside accelerate method

B. Missing self in accelerate method parameter

C. Incorrect print statement syntax

D. No error, code runs fine

Solution

1. Step 1: Check method parameter

   accelerate has self parameter, so it can access attributes.

2. Step 2: Identify attribute update

   Inside accelerate, speed += 10 tries to update speed but misses self. It should be self.speed += 10.

3. Final Answer:

   Using speed without self inside accelerate method -> Option A

4. Quick Check:

   Use self.speed to modify attribute [OK]

Hint: Always use self.attribute to change object state inside methods [OK]

Common Mistakes:

• Forgetting self. before attribute inside methods
• Thinking print syntax is wrong
• Assuming missing self parameter causes error here

5. You want to keep track of how many times a method use() is called on an object. Which is the best way to modify the object state to do this?

hard

A. Delete the object after each use() call

B. Print a message every time use() is called

C. Create a new object each time use() is called

D. Add an attribute count initialized to 0 and increase it inside use()

Solution

1. Step 1: Understand tracking calls

   To count calls, store a number in the object that updates each time.

2. Step 2: Modify state properly

   Initialize an attribute count = 0, then increase it by 1 inside use() method.

3. Final Answer:

   Add an attribute count initialized to 0 and increase it inside use() -> Option D

4. Quick Check:

   Use attribute to track count [OK]

Hint: Use attribute counter updated inside method to track calls [OK]

Common Mistakes:

• Just printing without storing count
• Creating new objects instead of updating state
• Deleting object removes all state