Notification System Project

Real-world applications often need to deliver messages through multiple channels — email, SMS, push notifications, and chat platforms like Slack. When each channel has its own sending and validation logic, abstraction lets you add new channels without modifying the code that dispatches messages. This project exercises the Abstract Base Class patterns introduced earlier in the chapter.

Build a multi-channel notification system using abstraction.

Requirements

Abstract NotificationChannel

Define NotificationChannel as an abstract base class using Python's abc module. It must declare two abstract methods:

• send(recipient, message) — Deliver the message to the given recipient via this channel. Raise an exception if delivery fails.
• validate_recipient(recipient) — Check that the recipient string is valid for this channel (e.g., email format, phone number format). Return True or False.

Implementations

Each concrete class inherits from NotificationChannel and implements both abstract methods with channel-specific logic:

• EmailNotification — Validate email format, simulate sending via SMTP.
• SMSNotification — Validate phone number format, simulate sending via SMS gateway.
• PushNotification — Validate device token, simulate push delivery.
• SlackNotification — Validate Slack channel or user ID, simulate webhook post.

NotificationService

• register_channel(channel) — Register a NotificationChannel instance for use.
• send_notification(recipients, message, channels) — Send the message to all recipients via the specified channels. Handle per-channel failures gracefully by logging the error and continuing with remaining channels.
• Sends via all registered channels if no specific channels are specified.

Use Python's abc module to define NotificationChannel as an abstract base class. Each concrete channel must implement all abstract methods. The NotificationService should depend only on the NotificationChannel interface, not on any concrete implementation.