python-design-patterns

To refactor a monolithic Python request handler, split HTTP parsing, business logic, and persistence into independent handler, service, and repository layers. This separation of concerns enforces single responsibility, reducing coupling so each layer can be tested and changed independently.

Use composition over inheritance in Python when replacing brittle inheritance hierarchies with composed collaborators. This approach reduces coupling and utilizes dependency injection, making dependencies easier to inject and test independently.

Reduce coupling and improve testability in Python backend projects by applying single responsibility and separation of concerns. Refactoring handlers into distinct service and repository layers with dependency injection keeps functions focused and modules independent.

You need to abstract Python code when there is clear repetition, following the Rule of Three. Prefer simple solutions initially and delay abstraction to avoid overly complex code, ensuring maintainability through practical design principles.

Dependency injection works for separating concerns in Python by injecting composed collaborators into services rather than hardcoding them. This replaces brittle inheritance, reduces coupling, and makes business rules easier to test independently.