Purpose of constructors in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constructor method in a Python class.

Python

class Car:
    def [1](self):
        self.color = 'red'

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

A__init__

Binit

Cstart

Dconstructor

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'init' without underscores

Using 'constructor' as method name

Using 'start' instead of '__init__'

The constructor method in Python is named __init__. It runs when a new object is created.

2fill in blank

medium

Complete the constructor to accept a parameter and assign it to an instance variable.

Python

class Person:
    def __init__(self, name):
        self.[1] = name

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

Aself

BName

Cname

Dperson

Attempts:

3 left

💡 Hint

Common Mistakes

Using capitalized 'Name' which is different

Assigning to 'self.self' or 'self.person'

Forgetting to use 'self.' before the variable

The instance variable should match the parameter name to store the value properly.

3fill in blank

hard

Fix the error in the constructor method name.

Python

class Animal:
    def [1](self):
        self.type = 'mammal'

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

A__init__

Binit__

C_init_

Dinitialize

Attempts:

3 left

💡 Hint

Common Mistakes

Using single underscores or missing underscores

Using 'initialize' instead of '__init__'

Misspelling the method name

The constructor must be named exactly __init__ with double underscores on both sides.

4fill in blank

hard

Fill both blanks to create a constructor that sets two instance variables.

Python

class Book:
    def __init__(self, title, author):
        self.[1] = title
        self.[2] = author

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

Atitle

Bname

Cauthor

Dwriter

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names like 'name' or 'writer' for instance variables

Mixing up the order of variables

Forgetting 'self.' before variable names

The instance variables should match the parameter names to store the values correctly.

5fill in blank

hard

Fill all three blanks to create a constructor that initializes three instance variables.

Python

class Laptop:
    def __init__(self, brand, model, price):
        self.[1] = brand
        self.[2] = model
        self.[3] = price

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

Abrand

Bmodel

Cprice

Dcost

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cost' instead of 'price' for the last variable

Mixing variable names or forgetting 'self.'

Assigning wrong parameters to variables

The instance variables should match the constructor parameters to store the values properly.

Practice

1. What is the main purpose of a constructor in a Python class?

easy

A. To print information about the class

B. To delete objects when they are no longer needed

C. To initialize new objects with starting values

D. To create new functions inside the class

Solution

1. Step 1: Understand what a constructor does

   A constructor is a special method that runs when a new object is created.

2. Step 2: Identify the purpose of initialization

   It sets up the object with initial values so it is ready to use.

3. Final Answer:

   To initialize new objects with starting values -> Option C

4. Quick Check:

   Constructor = initialize objects [OK]

Hint: Constructors set starting values when creating objects [OK]

Common Mistakes:

• Confusing constructors with methods that delete objects
• Thinking constructors print information automatically
• Believing constructors create new functions

2. Which of the following is the correct way to define a constructor in a Python class?

easy

A. def __init__(self):

B. def constructor(self):

C. def init(self):

D. def __start__(self):

Solution

1. Step 1: Recall Python constructor syntax

   Python uses a special method named __init__ to define constructors.

2. Step 2: Match the exact method name

   The method must be named exactly __init__ with double underscores before and after.

3. Final Answer:

   def __init__(self): -> Option A

4. Quick Check:

   Constructor method = __init__ [OK]

Hint: Constructor method is always named __init__ in Python [OK]

Common Mistakes:

• Using 'constructor' or 'init' without underscores
• Using wrong method names like __start__
• Forgetting double underscores before and after init

3. What will be the output of this code?

class Dog:
    def __init__(self, name):
        self.name = name
    def bark(self):
        return f"{self.name} says Woof!"

my_dog = Dog("Buddy")
print(my_dog.bark())

medium

A. Buddy says Woof!

B. Woof!

C. my_dog says Woof!

D. Error: missing argument

Solution

1. Step 1: Understand the constructor usage

   The constructor sets self.name to "Buddy" when my_dog is created.

2. Step 2: Check the bark method output

   bark returns a string with self.name followed by "says Woof!" so it returns "Buddy says Woof!".

3. Final Answer:

   Buddy says Woof! -> Option A

4. Quick Check:

   Constructor sets name, bark uses it [OK]

Hint: Constructor sets name; bark prints name with Woof [OK]

Common Mistakes:

• Ignoring the name argument in constructor
• Expecting bark to print only 'Woof!'
• Thinking my_dog is printed instead of its name

4. Identify the error in this class definition:

class Car:
    def __init__(self, model):
        model = model

my_car = Car("Tesla")
print(my_car.model)

medium

A. The print statement should be print(model)

B. The constructor name is incorrect

C. The class is missing a return statement

D. The constructor does not assign model to self.model

Solution

1. Step 1: Check constructor assignment

   The constructor assigns model to local variable model, not to self.model.

2. Step 2: Understand attribute access

   Without self.model, the object has no model attribute, causing an error on print.

3. Final Answer:

   The constructor does not assign model to self.model -> Option D

4. Quick Check:

   Use self.model = model to store attribute [OK]

Hint: Always assign to self.attribute inside __init__ [OK]

Common Mistakes:

• Assigning to local variable instead of self.attribute
• Thinking constructor name is wrong
• Expecting print(model) to work outside class

5. You want to create a class Book that stores title and author. Which constructor correctly initializes these attributes and allows creating a Book object with both values?

hard

A. def __init__(self, author):
self.title = title
self.author = author

B. def __init__(self, title, author):
self.title = title
self.author = author

C. def __init__(self, title):
self.title = title
self.author = author

D. def __init__(self):
title = ''
author = ''

Solution

1. Step 1: Check parameters needed

   Both title and author must be passed to the constructor to initialize attributes.

2. Step 2: Verify attribute assignment

   Constructor must assign both self.title and self.author from parameters.

3. Final Answer:

   def __init__(self, title, author): self.title = title self.author = author -> Option B

4. Quick Check:

   Constructor with all attributes assigned = def __init__(self, title, author): self.title = title self.author = author [OK]

Hint: Constructor needs all attributes as parameters and assigns them [OK]

Common Mistakes:

• Missing parameters for all attributes
• Assigning attributes without parameters
• Using local variables instead of self attributes