Python Pub/Sub System

A simple implementation of a Publisher-Subscriber (Pub/Sub) messaging pattern in Python. This system allows for decoupled communication between publishers and subscribers through topics.

System Architecture

Core Components

Models

• models/subscriber.py: Defines the Subscriber class that represents message consumers

  • __init__(self, id): Initializes subscriber with unique ID
  • get_id(): Returns subscriber's unique identifier

• models/topic.py: Implements Topic class to manage message queues and subscriptions

  • __init__(self, name): Creates topic with given name
  • add_message(message): Adds message to topic's queue
  • get_messages(): Returns all messages in topic
  • get_last_message(): Returns most recent message
  • add_subscriber(subscriber): Adds subscriber to topic
  • remove_subscriber(subscriber): Removes subscriber from topic

• models/publisher.py: Contains Singleton Publisher class for message producers

  • __new__(cls): Ensures single publisher instance
  • __init__(): Initializes publisher
  • publish(message, topic): Publishes message to specific topic
  • publish_to_all(message): Publishes message to all available topics

Services

• services/publishService.py: Handles message publishing operations

  • publish_to_topic(message, topic_name): Publishes message to specific topic
  • publish_to_all(message): Uses Singleton publisher to broadcast message to all topics

• services/subscribeService.py: Manages subscription operations and message retrieval

  • subscribe(subscriber, topic_name): Subscribes user to topic
  • unsubscribe(subscriber, topic_name): Removes subscription
  • read_all_message(subscriber, topic_name): Retrieves all messages from topic
  • read_last_message(subscriber, topic_name): Gets most recent message from topic

Repository

• repository/topicsRepository.py: Manages topic storage and operations
  • create_topic(topic_name): Creates new topic
  • get_topic(topic_name): Retrieves specific topic
  • get_all_topics(): Returns all available topics
  • delete_topic(topic_name): Removes topic

Main Module

• pubsub.py: Entry point demonstrating the system's functionality
  • Creates test topics and subscribers
  • Demonstrates subscription management
  • Shows message publishing and retrieval

Singleton Publisher Pattern

The system implements a Singleton pattern for the Publisher class, ensuring:

• Only one publisher instance exists throughout the application
• Centralized message distribution
• Consistent message broadcasting to all topics
• Thread-safe publishing operations

How It Works

1. Topic Management

   • Topics are created through TopicRepository
   • Each topic maintains its own message queue
   • Multiple subscribers can subscribe to the same topic

2. Publishing

   • Single publisher instance handles all publishing operations
   • Publishers can send messages to specific topics
   • Global broadcast capability to all topics
   • Messages are stored in topic-specific queues

3. Subscribing

   • Subscribers can subscribe to multiple topics
   • The SubscribeService manages subscriptions
   • Subscribers can:
     • Read all messages from a topic
     • Read only the last message from a topic