DIP

Motivation

DIP solves the problem of important business logic depending directly on low-level details. If core policy knows about databases, email vendors, or payment SDKs, changing infrastructure becomes risky.

Where it fits

DIP belongs to SOLID and software design. It is closely related to dependency injection, clean architecture, and ports/adapters style boundaries.

class CheckoutService:  def checkout(self, order):      payment = StripePaymentGateway()      repository = PostgresOrderRepository()      payment.charge(order.total)      repository.save(order)

class CheckoutService:  def __init__(self, payment_gateway, order_repository):      self.payment_gateway = payment_gateway      self.order_repository = order_repository  def checkout(self, order):      self.payment_gateway.charge(order.total)      self.order_repository.save(order)

Common mistakes

• Confusing DIP with a dependency injection framework.
• Creating abstractions for things that are unlikely to vary.