clean-architecture-python

Structure Python services into hexagonal architecture by separating domain, application, infrastructure, and API layers. This enforces strict inward-facing dependency rules so FastAPI routes act as adapters without leaking infrastructure concerns into the business domain.

Keep the domain layer pure by defining abstract ports and using concrete adapters for persistence and external APIs. Dependency inversion ensures your domain entities and use cases remain free of external imports like ORMs or framework specific dependencies.

Dependency injection in clean architecture works through container wiring to provide use cases with repository implementations. This allows you to isolate domain and application logic for unit testing while enabling integration testing for infrastructure adapters like Postgres.

The best way to test business logic separated from infrastructure is by applying the repository pattern with abstract ports. This enables rapid unit tests for domain rules and use cases while isolating slow integration tests for database and API adapters.

You need clean architecture when your Python backend mixes business logic with infrastructure and transport concerns. If your service uses FastAPI, ORMs, and asynchronous IO and suffers from poor testability and maintainability, hexagonal architecture enforces necessary layer boundaries.

Yes, you can use the repository pattern with asynchronous IO and ORMs by implementing abstract repository ports and concrete database adapters. This keeps your domain layer free of ORM imports while supporting asynchronous database operations in the infrastructure layer.