Python Fastapi

Full standards in python-fastapi.md. Always-on summary:

Routing and structure:

• Use APIRouter with prefix="/users" (explicit prefix=) and tags; mount routers in main.py with app.include_router()
• Return typed response models via response_model= — never return raw dicts from endpoints
• Use status_code=status.HTTP_201_CREATED (or appropriate) on every route decorator

Pydantic models:

• Separate CreateSchema, UpdateSchema, and ReadSchema; never expose ORM models directly
• Use model_config = ConfigDict(from_attributes=True) for ORM serialization
• Validate at the boundary — put business logic in services, not schemas

Dependency injection:

• Inject DB sessions via Depends(get_db) — never create sessions inside route functions
• Use Annotated[T, Depends(fn)] syntax (FastAPI 0.95+) for cleaner signatures
• Raise HTTPException in dependencies; FastAPI propagates them automatically

Async:

• Use async def for all I/O-bound endpoints; use def for CPU-bound work (runs in threadpool)
• Never call blocking I/O (requests, psycopg2, etc.) from async def — use async drivers

OpenAPI and error handling:

• Add summary=, description=, and responses= to all public endpoints
• Define a global exception handler for unhandled errors; return {"detail": ...} envelopes

Never:

• Never import app directly in sub-modules — use APIRouter and mount
• Never use Optional[X] without a default; prefer X | None = None (Python 3.10+)
• Never block the event loop with synchronous sleeps — use await asyncio.sleep()

Related skills: error-handling, logging-standards, database-sql, api-conventions

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