FastAPI is a beautiful development experience. The "Fast" in FastAPI leads to a bit misleading thought process.
The development experience is fast, scaffolding is fast, documentation is fast. Its not just fast from performance POV.

@app.get("/")def home():    return {"message": "Hello, FastAPI!"}

Let's review what is happening here:

1. We import the FastAPI class and create an instance named app. This app object is the heart of our application.

2. @app.get("/") is a decorator. It tells FastAPI that the function below is responsible for handling GET requests on the path /.

3. We return a dictionary and FastAPI automatically converts it to JSON. No manual serialization needed.

Running the app:

Go to your terminal and type:

uvicorn main:app --reload

Here main is the file name and app is the FastAPI instance we created. The --reload flag restarts the server whenever we change the code. Use it only in development, not in production.

You should see something like:

INFO:     Uvicorn running on http://127.0.0.1:8000INFO:     Application startup complete.

Open http://127.0.0.1:8000 in your browser and you will see our JSON response. 🎉

Automatic Docs:

Now visit http://127.0.0.1:8000/docs
Surprise! FastAPI has generated interactive Swagger documentation for our API. We did not write a single line for this.