__init__ method behavior in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Python

class Car:
    def [1](self, make, model):
        self.make = make
        self.model = model

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

Aconstructor

Binit

C__init__

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'init' without underscores.

Using 'constructor' or other names instead of '__init__'.

The __init__ method is the special constructor method in Python classes. It runs when you create a new object.

2fill in blank

medium

Complete the code to create an instance of the class Car with make 'Toyota' and model 'Corolla'.

Python

my_car = Car([1], 'Corolla')

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

A'Toyota'

B'Honda'

C'Ford'

D'BMW'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the wrong string for the make.

Forgetting to use quotes around the string.

To create an object with make 'Toyota', pass the string 'Toyota' as the first argument.

3fill in blank

hard

Fix the error in the constructor method name to make the class work correctly.

Python

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

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

Ainitialize

B__init__

C_init_

Dinit__

Attempts:

3 left

💡 Hint

Common Mistakes

Using single underscores or misspelling the method name.

Using other names like 'initialize'.

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

4fill in blank

hard

Fill both blanks to complete the constructor that sets the attributes 'name' and 'age'.

Python

class Student:
    def __init__(self, name, age):
        self.[1] = name
        self.[2] = age

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

Aname

Bage

Cgrade

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing attribute names or using unrelated names like 'grade'.

Forgetting to use 'self.' before attribute names.

The attributes should match the parameter names to store the values correctly.

5fill in blank

hard

Fill all three blanks to complete the constructor that sets 'title', 'author', and 'pages' attributes.

Python

class Book:
    def __init__(self, title, author, pages):
        self.[1] = title
        self.[2] = author
        self.[3] = pages

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

Atitle

Bauthor

Cpages

Dpublisher

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect attribute names like 'publisher'.

Forgetting 'self.' before attribute names.

The constructor assigns each parameter to an attribute with the same name.

Practice

1.

What is the main purpose of the __init__ method in a Python class?

easy

A. To create a new class

B. To delete an object from memory

C. To print information about the class

D. To set up initial values for the object's attributes

Solution

1. Step 1: Understand the role of __init__

   The __init__ method runs automatically when an object is created to set up initial values.

2. Step 2: Compare options with this role

   Only To set up initial values for the object's attributes describes setting initial attribute values, which matches __init__'s purpose.

3. Final Answer:

   To set up initial values for the object's attributes -> Option D

4. Quick Check:

   __init__ sets initial values = A [OK]

Hint: Remember: __init__ sets starting info for objects [OK]

Common Mistakes:

• Thinking __init__ deletes objects
• Confusing __init__ with printing methods
• Believing __init__ creates classes

2.

Which of the following is the correct way to define an __init__ method inside a Python class?

class Car:
    ?

easy

A. def __init__(self, model):

B. def init(self, model):

C. def __start__(self, model):

D. def __init__(model):

Solution

1. Step 1: Check method name and parameters

   The method must be named exactly __init__ and include self as the first parameter.

2. Step 2: Compare options

   Only def __init__(self, model): uses the correct name and includes self properly.

3. Final Answer:

   def __init__(self, model): -> Option A

4. Quick Check:

   Correct __init__ syntax = D [OK]

Hint: Always include self as first parameter in __init__ [OK]

Common Mistakes:

• Omitting self parameter
• Misspelling __init__ method name
• Using wrong method names like init or __start__

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)

medium

A. Buddy

B. name

C. Dog

D. Error

Solution

1. Step 1: Understand object creation and attribute assignment

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

2. Step 2: Check the print statement

   Printing my_dog.name outputs the string "Buddy" stored in the attribute.

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Object attribute value = Buddy [OK]

Hint: Print object.attribute to see stored value from __init__ [OK]

Common Mistakes:

• Printing class name instead of attribute
• Expecting attribute name instead of value
• Assuming code causes error

4.

Find the error in this class definition:

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

p = Person("Alice")

medium

A. Wrong class name

B. Missing self parameter in __init__

C. Missing parentheses when creating object

D. No error

Solution

1. Step 1: Check __init__ method parameters

   The __init__ method must have self as the first parameter, but it is missing here.

2. Step 2: Identify impact of missing self

   Without self, self.name causes an error because self is undefined.

3. Final Answer:

   Missing self parameter in __init__ -> Option B

4. Quick Check:

   __init__ needs self first [OK]

Hint: Always put self as first __init__ parameter [OK]

Common Mistakes:

• Forgetting self in method parameters
• Thinking class name must change
• Missing parentheses when creating object

5.

Consider this class:

class Book:
    def __init__(self, title, author="Unknown"):
        self.title = title
        self.author = author

b1 = Book("Python 101")
b2 = Book("Learn AI", "Dr. Smith")
print(b1.author, b2.author)

What will be printed?

hard

A. Dr. Smith Unknown

B. Python 101 Learn AI

C. Unknown Dr. Smith

D. Error due to missing author argument

Solution

1. Step 1: Understand default parameter in __init__

   The author parameter has a default value "Unknown", so it is optional when creating an object.

2. Step 2: Analyze object creations

   b1 is created with only title, so author is "Unknown". b2 provides both title and author "Dr. Smith".

3. Step 3: Check print output

   Printing b1.author and b2.author prints "Unknown Dr. Smith".

4. Final Answer:

   Unknown Dr. Smith -> Option C

5. Quick Check:

   Default parameters fill missing values = A [OK]

Hint: Default values fill missing arguments in __init__ [OK]

Common Mistakes:

• Expecting error when argument is missing
• Mixing up title and author values
• Assuming both arguments are always required