Typed Python changes the API story

Welcome! I'm Param. In this course we scaffold a production-shaped FastAPI service together, pulling working code from two real workshop repos: streaming-llm-fastapi for the LLM service shape, and rag-chromadb for the RAG patterns. By the end you will have a running server with typed endpoints, Pydantic contracts, a lifespan that loads a model once, and a Dockerized dev loop.

Before we write any code, let us answer the question every Python developer asks: why FastAPI and not Flask or Django? The answer comes down to types. FastAPI treats your type hints as the source of truth for validation, serialization, and documentation. Flask and Django treat them as comments.

Three Python API frameworks

FastAPI bakes types into the request cycle. Flask and Django make you bolt them on.

You can write type hints in Flask, but Flask will not enforce them. You still have to call request.get_json(), validate the shape yourself, and return tuples of dict and status code. FastAPI reads the type hint on your parameter, validates the body against it, and rejects bad payloads with a 422 before your function even runs. The hints stop being decorative and start being the contract.

Quiz: Quiz

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