FastAPI

Python's fastest-growing API framework — built on async Python and type hints, it generates OpenAPI docs automatically and rivals Node.js in raw performance.

FastAPI is the fastest-growing Python web framework, designed for building high-performance REST APIs using modern Python features: async/await, type hints with Pydantic, and automatic OpenAPI/Swagger documentation generation. It outperforms Django and Flask in raw throughput and has become the default choice for new Python API projects in startups and data-heavy organizations. FastAPI is particularly common in AI and ML serving contexts — its async support and tight Pydantic integration make it ideal for wrapping ML models and data pipelines as APIs. It has overtaken Flask in many popularity metrics and is increasingly listed alongside Django in Python backend job postings.

Typical time to job-readiness: ~3 weeks.

Learning FastAPI

Beginner

Build a simple CRUD API: define Pydantic models for request/response validation, create path operations (GET, POST, PUT, DELETE), and explore the auto-generated Swagger UI at /docs. Understand how FastAPI uses Python type hints to drive validation and documentation.

Intermediate

SQLAlchemy with async sessions for database access, dependency injection for shared resources (database connections, auth), background tasks, and JWT authentication middleware. Learn how Pydantic v2 works — it is central to how FastAPI validates everything.

Advanced

Async performance optimization, WebSockets for real-time features, custom middleware, and deploying with Uvicorn/Gunicorn behind Nginx. ML engineers often use FastAPI to serve model predictions — be ready to discuss request batching, model loading on startup, and handling inference latency.

Key concepts

  • Path operations decorated with @app.get, @app.post, etc. — the primary way to define endpoints
  • Pydantic models for request/response validation — type hints become runtime validation and docs
  • Dependency injection: inject shared resources (DB sessions, auth tokens) into any route with Depends()
  • Async/await: FastAPI is ASGI-native; async route functions handle concurrent requests without blocking
  • Auto-generated docs: Swagger UI at /docs and ReDoc at /redoc with zero configuration
  • Uvicorn: the ASGI server that runs FastAPI; use Gunicorn with Uvicorn workers in production

Common interview topics

  • What makes FastAPI faster than Django or Flask for API development
  • How does Pydantic validation work in FastAPI
  • Explain FastAPI's dependency injection system
  • How would you add authentication to a FastAPI application
  • How do you handle async database queries in FastAPI

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