Python + FastAPI Best Practices — Quick Reference

Layered Architecture

Router → Service → Repository → Database. Each layer only calls the one below it.

See code-patterns.md for full project structure and layer examples.

Pydantic v2

Separate Create/Update/Response schemas. Use ConfigDict(from_attributes=True) for ORM integration. Use str | None syntax (not Optional[str]).

See code-patterns.md for schema examples.

Async Patterns

async def for I/O routes, plain def for CPU-bound. Use lifespan context manager (not on_event). Use httpx.AsyncClient for external HTTP calls.

See code-patterns.md for async examples.