Instance methods in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of instance method call

What is the output of this Python code?

Python

class Car:
    def __init__(self, brand):
        self.brand = brand
    def show_brand(self):
        return f"This car is a {self.brand}."

my_car = Car("Toyota")
print(my_car.show_brand())

A Error: show_brand() missing 1 required positional argument

B This car is a Toyota.

C Toyota

D This car is a brand.

💡 Hint

Look at how the instance method uses self to access the brand attribute.

The method show_brand uses self.brand to get the brand of the car instance. Since my_car.brand is 'Toyota', the output is 'This car is a Toyota.'.

❓ Predict Output

intermediate

Instance method modifying attribute

What will be the value of x.speed after running this code?

Python

class Bike:
    def __init__(self):
        self.speed = 0
    def accelerate(self, amount):
        self.speed += amount

x = Bike()
x.accelerate(10)

A 10

B 0

C Error: accelerate() missing 1 required positional argument

D None

💡 Hint

The accelerate method adds the amount to the speed attribute.

The accelerate method increases the speed attribute by the given amount. Initially speed is 0, after calling accelerate(10), speed becomes 10.

❓ Predict Output

advanced

Instance method with default argument

What is the output of this code snippet?

Python

class Counter:
    def __init__(self):
        self.count = 0
    def add(self, n=1):
        self.count += n
        return self.count

c = Counter()
print(c.add())
print(c.add(5))

A 0\n5

B 1\n1

C 1\n6

D Error: add() missing 1 required positional argument

💡 Hint

The add method increases count by n, defaulting to 1 if no argument is given.

First call c.add() adds 1 to count (0+1=1). Second call c.add(5) adds 5 (1+5=6). So outputs are 1 and 6.

❓ Predict Output

advanced

Instance method calling another instance method

What will this code print?

Python

class Person:
    def __init__(self, name):
        self.name = name
    def greet(self):
        return f"Hello, {self.name}!"
    def welcome(self):
        return self.greet() + " Welcome to the platform."

p = Person("Alice")
print(p.welcome())

A Alice Welcome to the platform.

B Hello, welcome to the platform.

C Error: greet() missing 1 required positional argument

D Hello, Alice! Welcome to the platform.

💡 Hint

The welcome method calls greet and adds more text.

The welcome method calls greet(), which returns 'Hello, Alice!'. Then it adds ' Welcome to the platform.' resulting in the full greeting.

🧠 Conceptual

expert

Understanding self in instance methods

Which statement about the use of self in instance methods is correct?

A self refers to the instance on which the method is called and is passed automatically.

B self is a keyword in Python that refers to the current class.

C self must be explicitly passed when calling an instance method.

D self is optional and can be omitted in instance method definitions.

💡 Hint

Think about how Python passes the instance to methods.

self is a conventional name for the first parameter of instance methods. It refers to the instance and is passed automatically by Python when calling the method.