Pub/sub pattern in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the main component that receives messages from publishers.

HLD

class [1]:
    def __init__(self):
        self.subscribers = []

    def subscribe(self, subscriber):
        self.subscribers.append(subscriber)

    def publish(self, message):
        for subscriber in self.subscribers:
            subscriber.receive(message)

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

ABroker

BPublisher

CSubscriber

DListener

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the Broker with Publisher or Subscriber roles.

Using 'Listener' which is not a standard term in pub/sub.

The Broker is the central component that receives messages from publishers and forwards them to subscribers.

2fill in blank

medium

Complete the code to define the method that subscribers use to receive messages.

HLD

class Subscriber:
    def receive(self, [1]):
        print(f"Received: {message}")

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

Amsg

Bmessage

Cdata

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name different from the one used in the method body.

Choosing generic names that don't match the code.

The method parameter should be named message to match the print statement and represent the incoming data.

3fill in blank

hard

Fix the error in the publish method to correctly send messages to subscribers.

HLD

def publish(self, message):
    for subscriber in self.subscribers:
        subscriber.[1](message)

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

Asend

Breceive

Cnotify

Dpublish

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a non-existent method like 'send' or 'notify' on subscribers.

Using 'publish' which is a publisher's method.

The receive method is called on subscribers to deliver the message.

4fill in blank

hard

Fill both blanks to create a dictionary that maps topics to subscriber lists.

HLD

class Broker:
    def __init__(self):
        self.topics = [1]  # Initialize empty dictionary

    def subscribe(self, topic, subscriber):
        if topic not in self.topics:
            self.topics[topic] = [2]  # Initialize list for new topic
        self.topics[topic].append(subscriber)

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

A{}

B[]

Cset()

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using a set instead of a list for subscribers.

Initializing topics as None or list instead of dictionary.

The topics attribute is a dictionary ({}), and each topic maps to a list ([]), which holds subscribers.

5fill in blank

hard

Fill all three blanks to implement publishing a message to all subscribers of a topic.

HLD

def publish(self, topic, message):
    subscribers = self.topics.get([1], [2])
    for subscriber in subscribers:
        subscriber.[3](message)

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

Atopic

B[]

Creceive

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong default value in get method.

Calling a wrong method on subscriber.

We get the list of subscribers for the topic, defaulting to an empty list [] if none exist, then call receive on each subscriber.