python-fastapi-coding-conventionslisted

# Coding Conventions Style, naming, error handling, logging, configuration, database, and API conventions for Python/FastAPI backends. --- ## Core Development Philosophy **Choose the simplest solution that works.** Complexity is a liability — every abstraction, extra class, and indirection must justify itself. Apply these principles in order: - **KISS** — Choose the straightforward path. Don't split functionality into multiple classes when one handles it. Don't create abstractions speculatively. - **YAGNI** — Implement only what's needed now. Resist "we might need this later." - **Single Responsibility** — Each function, class, and module has one clear purpose. - **Dependency Inversion** — Inner layers must not depend on outer layers. Domain logic never imports from API or persistence. - **Open/Closed** — Extend behaviour by adding code, not by modifying existing code. --- ## Layered Architecture Every feature touches four layers. Know which layer owns which responsibility: ``` API (routes, schemas, middleware) ↓ Services (business logic, orchestration) ↓ Repositories (data access only) ↓ Domain (entities, exceptions, business rules) ``` **API layer** — HTTP in, HTTP out. Routes call services. Middleware handles cross-cutting concerns (auth, logging). No business logic here. **Service layer** — Orchestrates repositories and domain logic. Raises domain exceptions. Never touches the DB directly. **Repository layer** — Thin data access. No business logic. Retur