CODESAMPLE

Dependency Injection - Python

Dependency Injection Python

Dependency Injection (DI) is a design pattern where a class receives its dependencies from external sources rather than creating them itself. This promotes loose coupling, making the class more testable, reusable, and maintainable. Our Python example utilizes constructor injection – dependencies are provided through the class constructor. The NotificationService depends on a MessageSender. Instead of NotificationService creating a MessageSender, we inject an instance of it. This is idiomatic Python due to its flexible nature and easy handling of objects as first-class citizens, avoiding tight coupling often seen in more statically typed languages. Using type hints enhances readability and allows for static analysis.

from abc import ABC, abstractmethod
from typing import Protocol

class MessageSender(Protocol):
    """Protocol for message sending."""
    def send(self, message: str) -> None:
        """Sends a message."""
        ...


class EmailSender(MessageSender):
    def send(self, message: str) -> None:
        print(f"Sending email: {message}")


class SMSSender(MessageSender):
    def send(self, message: str) -> None:
        print(f"Sending SMS: {message}")


class NotificationService:
    """
    A service that sends notifications via a given message sender.
    Demonstrates Dependency Injection.
    """
    def __init__(self, message_sender: MessageSender):
        self.message_sender = message_sender

    def send_notification(self, message: str) -> None:
        self.message_sender.send(message)


# Usage:
if __name__ == "__main__":
    email_sender = EmailSender()
    notification_service_email = NotificationService(email_sender)
    notification_service_email.send_notification("Hello via email!")

    sms_sender = SMSSender()
    notification_service_sms = NotificationService(sms_sender)
    notification_service_sms.send_notification("Hello via SMS!")