Python / FastAPI Interview Questions
What are the most important FastAPI best practices for a production-ready API?
A well-architected FastAPI project follows consistent patterns across structure, validation, security, and operations. Here is a consolidated reference.
| Area | Best Practice |
|---|---|
| Project structure | Separate concerns: routers/, models/, schemas/, dependencies/, services/ |
| Pydantic models | Separate Input/Output models; never return password fields; use Field() for constraints |
| Dependencies | Use Depends() for DB sessions, auth, pagination — keep routes thin |
| Authentication | JWT with short expiry + refresh tokens; hash passwords with bcrypt/argon2 |
| Database | Async SQLAlchemy + asyncpg; connection pool sized to workers; run Alembic in CI/CD |
| Error handling | Custom exception handlers for consistent error format; never expose stack traces |
| Testing | 100% route coverage with TestClient; override dependencies for isolation |
| Configuration | pydantic-settings + .env; never hardcode secrets; use secret managers in prod |
| Deployment | Gunicorn + UvicornWorker; non-root Docker user; health check endpoint |
| Observability | Structured JSON logs; /metrics for Prometheus; distributed tracing with OpenTelemetry |
| Docs | Meaningful summaries/descriptions; hide /docs in production; version the API |
# Recommended project layout
# .
# ├── app/
# │ ├── main.py # FastAPI() instance, lifespan, include_router
# │ ├── config.py # pydantic-settings Settings class
# │ ├── database.py # engine, AsyncSessionLocal, Base
# │ ├── dependencies.py # get_db, get_current_user, pagination
# │ ├── routers/
# │ │ ├── users.py # APIRouter for /users
# │ │ └── items.py # APIRouter for /items
# │ ├── models/
# │ │ └── user.py # SQLAlchemy ORM models
# │ ├── schemas/
# │ │ └── user.py # Pydantic in/out schemas
# │ └── services/
# │ └── user_service.py # business logic, DB queries
# ├── tests/
# │ ├── conftest.py # fixtures, TestClient
# │ └── test_users.py
# ├── alembic/ # migrations
# ├── Dockerfile
# ├── docker-compose.yml
# └── requirements.txt
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