* **Facile**: Progettato per essere facile da usare e imparare. Si riduce il tempo da dedicare alla lettura della documentazione.
* **Sintentico**: Minimizza la duplicazione di codice. Molteplici funzionalità, ognuna con la propria dichiarazione dei parametri. Meno errori.
* **Robusto**: Crea codice pronto per la produzione con documentazione automatica interattiva.

    "paid": true
}
```

and it would expect a response from that *external API* with a JSON body like:

```JSON
{
    "ok": true
}
```

!!! tip
    Notice how the callback URL used contains the URL received as a query parameter in `callback_url` (`https://www.external.org/events`) and also the invoice `id` from inside of the JSON body (`2expen51ve`).

### Add the callback router

* `$` : se termine directement ensuite, n'a pas d'autres caractères après `fixedquery`.

Si vous vous sentez perdu avec le concept d'**expression régulière**, pas d'inquiétudes. Il s'agit d'une notion difficile pour beaucoup, et l'on peut déjà réussir à faire beaucoup sans jamais avoir à les manipuler.

Mais si vous décidez d'apprendre à les utiliser, sachez qu'ensuite vous pouvez les utiliser directement dans **FastAPI**.

            "name": "The Foo live"
        },
        {
            "url": "http://example.com/dave.jpg",
            "name": "The Baz"
        }
    ]
}
```

!!! info
    Notice how the `images` key now has a list of image objects.

## Deeply nested models

You can define arbitrarily deeply nested models:

=== "Python 3.10+"

    ```Python hl_lines="7  12  18  21  25"

And to communicate using WebSockets with your backend you would probably use your frontend's utilities.

Or you might have a native mobile application that communicates with your WebSocket backend directly, in native code.

Or you might have any other way to communicate with the WebSocket endpoint.

---

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="22"
    {!> ../../../docs_src/dependencies/tutorial005.py!}
    ```

!!! info
    Notice that we are only declaring one dependency in the *path operation function*, the `query_or_cookie_extractor`.

read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

This way you write shared code once and **FastAPI** takes care of calling it for your *path operations*.

!!! check
    Notice that you don't have to create a special class and pass it somewhere to **FastAPI** to "register" it or anything similar.

    You just pass it to `Depends` and **FastAPI** knows how to do the rest.

    ```

=== "Python 3.8+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/query_params_str_validations/tutorial002_an.py!}
    ```

Notice that the default value is still `None`, so the parameter is still optional.

    By doing it this way, we can put it in a `with` block, and that way, ensure that it is closed after finishing.

!!! tip
    Notice that here as we are using standard `open()` that doesn't support `async` and `await`, we declare the path operation with normal `def`.

### `FileResponse`

Asynchronously streams a file as the response.

Und um über WebSockets mit Ihrem Backend zu kommunizieren, würden Sie wahrscheinlich die Werkzeuge Ihres Frontends verwenden.

Oder Sie verfügen möglicherweise über eine native Mobile-Anwendung, die direkt in nativem Code mit Ihrem WebSocket-Backend kommuniziert.

Oder Sie haben andere Möglichkeiten, mit dem WebSocket-Endpunkt zu kommunizieren.

---