Why FastAPI, and what we build

Goal

Know what FastAPI gives you, what Shelf does, and how the next eleven chapters fit together.

What FastAPI is

FastAPI is a Python framework for building HTTP APIs. You write normal Python functions with type hints, and FastAPI turns those hints into three things at once:

• Validation. Wrong input is rejected before your code runs.
• Conversion. "42" in a URL becomes the integer 42 in your function.
• Documentation. A live, clickable API page at /docs, always in sync with the code.

It is built on two solid libraries: Starlette (the web part) and Pydantic (the data part).

What we build: Shelf

Shelf keeps a reading list. Each book has a title, an author, a status (want, reading or done), an optional 1 to 5 rating, and some tags.

Small enough to finish in an afternoon, real enough to ship: it has a database, auth, tests, logs, error handling and a Docker image.

The map

api/
  app/
    main.py         create_app(): wires everything together
    config.py       settings from the environment
    db.py           database engine and sessions
    models.py       tables (SQLAlchemy)
    schemas.py      request and response shapes (Pydantic)
    deps.py         dependencies: session, pagination, API key
    errors.py       one helpful error format
    middleware.py   request ids and access logs
    routers/        health.py, books.py, stats.py
  tests/            pytest, one fresh database per test
  Dockerfile

Every file starts with a comment that names the chapter it belongs to.

Check it works

Nothing to run yet. Read the table above and predict: what should GET /books/999 return when there is no book 999? You will find out in chapter 07.

Exercise

Think of one thing you would track with an API like this (films, recipes, gym sessions). Keep it in mind; every exercise works for your idea too.