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Python / FastAPI Basics 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.

FastAPI Production Best Practices
AreaBest Practice
Project structureSeparate concerns: routers/, models/, schemas/, dependencies/, services/
Pydantic modelsSeparate Input/Output models; never return password fields; use Field() for constraints
DependenciesUse Depends() for DB sessions, auth, pagination — keep routes thin
AuthenticationJWT with short expiry + refresh tokens; hash passwords with bcrypt/argon2
DatabaseAsync SQLAlchemy + asyncpg; connection pool sized to workers; run Alembic in CI/CD
Error handlingCustom exception handlers for consistent error format; never expose stack traces
Testing100% route coverage with TestClient; override dependencies for isolation
Configurationpydantic-settings + .env; never hardcode secrets; use secret managers in prod
DeploymentGunicorn + UvicornWorker; non-root Docker user; health check endpoint
ObservabilityStructured JSON logs; /metrics for Prometheus; distributed tracing with OpenTelemetry
DocsMeaningful 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

Why should you keep FastAPI route handlers 'thin' (minimal logic)?
What is the recommended password hashing approach in a FastAPI authentication system?

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