Creational patterns (Singleton, Factory, Builder) in Software Engineering - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to ensure only one instance of the class is created (Singleton pattern).

Software Engineering

class Singleton:
    _instance = None

    def __new__(cls):
        if cls._instance is [1]:
            cls._instance = super().__new__(cls)
        return cls._instance

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

AFalse

BNone

CTrue

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using False or 0 instead of None causes the check to fail.

The Singleton pattern ensures only one instance exists. Checking if _instance is None means no instance has been created yet.

2fill in blank

medium

Complete the Factory method to create a product based on the type.

Software Engineering

class Factory:
    def create_product(self, product_type):
        if product_type == 'A':
            return ProductA()
        elif product_type == 'B':
            return [1]()
        else:
            return None

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

AProductB

BProductC

CProductA

DProduct

Attempts:

3 left

💡 Hint

Common Mistakes

Returning ProductA or ProductC for product type 'B' is incorrect.

The Factory method returns an instance of the requested product type. For 'B', it should return ProductB().

3fill in blank

hard

Fix the error in the Builder pattern's build method to return the constructed object.

Software Engineering

class Builder:
    def __init__(self):
        self.product = Product()

    def build(self):
        self.product.add_part('Part1')
        self.product.add_part('Part2')
        return [1]

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

Aself

Bproduct

Cself.product

DProduct

Attempts:

3 left

💡 Hint

Common Mistakes

Returning self or Product class instead of the product instance.

The build method should return the constructed product object, which is stored in self.product.

4fill in blank

hard

Fill both blanks to complete the Singleton pattern's thread-safe instance retrieval.

Software Engineering

import threading

class Singleton:
    _instance = None
    _lock = threading.Lock()

    @classmethod
    def get_instance(cls):
        with cls.[1]:
            if cls._instance is [2]:
                cls._instance = cls()
        return cls._instance

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

Alock

Bmutex

CNone

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'mutex' instead of 'lock' or checking against False instead of None.

To make Singleton thread-safe, a lock is used. The lock attribute is named lock. The instance is checked against None to see if it needs creation.

5fill in blank

hard

Fill all three blanks to complete a dictionary comprehension that builds a product catalog with prices above zero.

Software Engineering

products = {'apple': 1.2, 'banana': 0, 'cherry': 2.5}
catalog = [1]: [2] for [3] in products.items() if [2] > 0

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

Aname

Bprice

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up keys and values or using inconsistent variable names.

The dictionary comprehension creates a new dictionary with product names as keys and prices as values, but only includes products with price greater than zero.