Constructor parameters in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constructor that takes one parameter 'name'.

Python

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

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

Aname

Bself

Cage

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'self' as a parameter name other than the first one.

Forgetting to include the parameter in the constructor.

The constructor method __init__ takes 'name' as a parameter to initialize the object.

2fill in blank

medium

Complete the code to assign the parameter 'age' to the instance variable.

Python

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

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

Aage

Bself.age

CPerson.age

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning self.age to itself instead of the parameter.

Using the class name instead of the parameter.

We assign the parameter 'age' to the instance variable self.age to store it in the object.

3fill in blank

hard

Fix the error in the constructor parameter to correctly accept two parameters: 'name' and 'age'.

Python

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

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

Aname age

Bname; age

Cname, age

Dself, name, age

Attempts:

3 left

💡 Hint

Common Mistakes

Separating parameters with spaces or semicolons instead of commas.

Including 'self' again in the parameter list.

Parameters must be separated by commas. The constructor always has 'self' as the first parameter, which is already there.

4fill in blank

hard

Fill both blanks to create a constructor that assigns 'name' and 'age' parameters to instance variables.

Python

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

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

Aname

Bage

Cself.name

Dself.age

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning instance variables to themselves instead of parameters.

Mixing up the parameter names.

The constructor assigns the parameters 'name' and 'age' to the instance variables self.name and self.age.

5fill in blank

hard

Fill all three blanks to create a constructor that assigns 'name', 'age', and 'city' parameters to instance variables.

Python

class Person:
    def __init__(self, name, age, city):
        self.name = [1]
        self.age = [2]
        self.city = [3]

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

Aname

Bage

Ccity

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'self' instead of parameter names on the right side.

Mixing up parameter names and instance variables.

The constructor assigns each parameter to its matching instance variable using self..

Practice

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

easy

A. To provide initial values to an object when it is created

B. To define methods that the class can use

C. To create global variables outside the class

D. To delete an object from memory

Solution

1. Step 1: Understand what constructor parameters do

   Constructor parameters allow you to pass values to an object when you create it, so it starts with specific data.

2. Step 2: Compare options with this understanding

   Only To provide initial values to an object when it is created describes this purpose correctly. Other options describe unrelated concepts.

3. Final Answer:

   To provide initial values to an object when it is created -> Option A

4. Quick Check:

   Constructor parameters = initial values [OK]

Hint: Constructor parameters set starting values for new objects [OK]

Common Mistakes:

• Confusing constructor parameters with methods
• Thinking constructor parameters delete objects
• Believing constructor parameters create global variables

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

easy

A. def __start__(self, name):

B. def constructor(name):

C. def init(self):

D. def __init__(self, name):

Solution

1. Step 1: Recall Python constructor syntax

   Python uses the special method named __init__ with self as the first parameter to define constructors.

2. Step 2: Check each option

   Only def __init__(self, name): uses the correct method name and includes self and a parameter.

3. Final Answer:

   def __init__(self, name): -> Option D

4. Quick Check:

   Constructor method = __init__ with self [OK]

Hint: Constructor method is always named __init__ with self first [OK]

Common Mistakes:

• Using wrong method names like constructor or init
• Omitting self parameter
• Using incorrect special method names

3. What will be the output of this code?

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

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

medium

A. Buddy says Woof!

B. Woof!

C. Dog says Woof!

D. Error: missing parameter

Solution

1. Step 1: Understand constructor parameter usage

   The constructor takes a name and assigns it to self.name. The object my_dog is created with name "Buddy".

2. Step 2: Analyze the speak method output

   The speak method returns a string using self.name, so it returns "Buddy says Woof!".

3. Final Answer:

   Buddy says Woof! -> Option A

4. Quick Check:

   Object name used in speak = Buddy says Woof! [OK]

Hint: Constructor sets name; speak uses it to print message [OK]

Common Mistakes:

• Ignoring the name parameter and expecting just 'Woof!'
• Confusing class name with instance name
• Assuming missing parameters cause error here

4. Identify the error in this class definition:

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

my_car = Car("red")

medium

A. Missing quotes around "red"

B. Missing self parameter in __init__ method

C. Cannot assign to self.color

D. Wrong method name, should be __start__

Solution

1. Step 1: Check __init__ method parameters

   The first parameter of __init__ must be self to refer to the instance. Here, self is missing.

2. Step 2: Confirm other parts are correct

   Method name __init__ is correct, assignment to self.color is valid, and "red" is properly quoted.

3. Final Answer:

   Missing self parameter in __init__ method -> Option B

4. Quick Check:

   __init__ first parameter = self [OK]

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

Common Mistakes:

• Forgetting self parameter
• Changing __init__ method name
• Misunderstanding self usage

5. You want to create a class Book that stores title and author when you create a new book object. Which constructor correctly sets these attributes?

hard

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

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

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

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

Solution

1. Step 1: Check parameter list and self usage

   The constructor must have self as first parameter, then title and author. def __init__(self, title, author): self.title = title self.author = author has this correct.

2. Step 2: Verify attribute assignment

   Attributes must be assigned as self.title = title and self.author = author to store values in the object. def __init__(self, title, author): self.title = title self.author = author does this correctly.

3. Final Answer:

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

4. Quick Check:

   Use self to assign attributes in __init__ [OK]

Hint: Use self.attribute = parameter inside __init__ [OK]

Common Mistakes:

• Omitting self parameter
• Assigning parameters to themselves instead of self
• Reversing assignment order