It is used by Pydantic and FastAPI to explicitly declare that a value is required.

///

This will let **FastAPI** know that this parameter is required.

### Required, can be `None`

You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.

To do that, you can declare that `None` is a valid type but still use `...` as the default:

Como cada modelo SQLModel também é um modelo Pydantic, você pode usá-lo nas mesmas **anotações de tipo** que usaria para modelos Pydantic.

Por exemplo, se você declarar um parâmetro do tipo `Hero`, ele será lido do **corpo JSON**.

Da mesma forma, você pode declará-lo como o **tipo de retorno** da função, e então o formato dos dados aparecerá na interface de documentação automática da API.

```Python hl_lines="31"
{!> ../../docs_src/security/tutorial002.py!}
```

////

Notice that we declare the type of `current_user` as the Pydantic model `User`.

This will help us inside of the function with all the completion and type checks.

/// tip

You might remember that request bodies are also declared with Pydantic models.

Here **FastAPI** won't get confused because you are using `Depends`.

///

So, the interactive docs will have all the information from these dependencies too:

<img src="/img/tutorial/dependencies/image01.png">

## Simple usage

If you look at it, *path operation functions* are declared to be used whenever a *path* and *operation* matches, and then **FastAPI** takes care of calling the function with the correct parameters, extracting the data from the request.

Além disso, em versões anteriores, o objeto `request` era passado como parte dos pares chave-valor no "context" dict para o Jinja2.

///

/// tip | "Dica"

Ao declarar `response_class=HTMLResponse`, a documentação entenderá que a resposta será HTML.

///

/// note | "Detalhes Técnicos"

Você também poderia usar `from starlette.templating import Jinja2Templates`.

///

/// tip | Dica

Para declarar o corpo de arquivos, você precisa utilizar `File`, do contrário os parâmetros seriam interpretados como parâmetros de consulta ou corpo (JSON) da requisição.

///

Os arquivos serão enviados como "form data".

  private final ImmutableList<Annotation> annotations;

  /**
   * An {@code AnnotatedType} instance, or {@code null} under Android VMs (possible only when using
   * the Android flavor of Guava). The field is declared with a type of {@code Object} to avoid
   * compatibility problems on Android VMs. The corresponding accessor method, however, can have the

* Les arguments nommés à passer à la fonction de tâche (`message="some notification"`).

## Injection de dépendances

Utiliser `BackgroundTasks` fonctionne aussi avec le système d'injection de dépendances. Vous pouvez déclarer un paramètre de type `BackgroundTasks` à différents niveaux : dans une *fonction de chemin*, dans une dépendance, dans une sous-dépendance...

 *
 * <p>The declaration methods must be public.
 */
@AndroidIncompatible // only used by android incompatible tests.
abstract class SubtypeTester implements Cloneable {

  /** Annotates a public method that declares subtype assertion. */
  @RequiredModifiers(Modifier.PUBLIC)
  @Retention(RetentionPolicy.RUNTIME)
  @Target(ElementType.METHOD)
  @interface TestSubtype {
    /** Suppresses the assertion on {@link TypeToken#getSubtype}. */

* The user types the `username` and `password` in the frontend, and hits `Enter`.
* The frontend (running in the user's browser) sends that `username` and `password` to a specific URL in our API (declared with `tokenUrl="token"`).
* The API checks that `username` and `password`, and responds with a "token" (we haven't implemented any of this yet).