* Controllo sulle annotazioni di tipo.
* Validazione dei dati:
    * Errori chiari e automatici quando i dati sono invalidi.
    * Validazione anche per gli oggetti JSON più complessi.
* <abbr title="anche noto come: serializzazione, parsing, marshalling">Conversione</abbr> dei dati di input: da risorse esterne a dati e tipi di Python. È possibile leggere da:
    * JSON.
    * Path parameters.
    * Query parameters.
    * Cookies.

    async def __call__(self, request: Request) -> Optional[str]:
        authorization = request.headers.get("Authorization")
        if not authorization:
            if self.auto_error:
                raise HTTPException(
                    status_code=HTTP_403_FORBIDDEN, detail="Not authenticated"
                )
            else:
                return None
        return authorization

!!! note "Technical Details"
    ASGI is a new "standard" being developed by Django core team members. It is still not a "Python standard" (a PEP), although they are in the process of doing that.

{!../../../docs_src/app_testing/tutorial001.py!}
```

!!! tip
    Notice that the testing functions are normal `def`, not `async def`.

    And the calls to the client are also normal calls, not using `await`.

    This allows you to use `pytest` directly without complications.

!!! note "Technical Details"
    You could also use `from starlette.testclient import TestClient`.

            "loc": [
                "path",
                "item_id"
            ],
            "msg": "value is not a valid integer",
            "type": "type_error.integer"
        }
    ]
}

```

被替换为了以下文本格式的错误信息：

```
1 validation error
path -> item_id
  value is not a valid integer (type=type_error.integer)

```

### `RequestValidationError` vs `ValidationError`

!!! warning
    Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.
    As these keys may not necessarily be part of the OpenAPI specification, some OpenAPI tools, for example [the OpenAPI validator](https://validator.swagger.io/), may not work with your generated schema.

## Recap

You can use Pydantic's `Field` to declare extra validations and metadata for model attributes.

<div class="termy">

```console
$ pip install "fastapi[all]"

---> 100%
```

</div>

...isso também inclui o `uvicorn`, que você pode usar como o servidor que rodará seu código.

!!! note "Nota"
    Você também pode instalar parte por parte.

    Isso é provavelmente o que você faria quando você quisesse lançar sua aplicação em produção:

    ```
    pip install fastapi
    ```

## Integrated middlewares

**FastAPI** includes several middlewares for common use cases, we'll see next how to use them.

!!! note "Technical Details"
    For the next examples, you could also use `from starlette.middleware.something import SomethingMiddleware`.

            "loc": [
                "path",
                "item_id"
            ],
            "msg": "value is not a valid integer",
            "type": "type_error.integer"
        }
    ]
}
```

👆 🔜 🤚 ✍ ⏬, ⏮️:

```
1 validation error
path -> item_id
  value is not a valid integer (type=type_error.integer)
```

#### `RequestValidationError` 🆚 `ValidationError`

!!! warning

```JSON
{
  "item": "The Foo Wrestlers"
}
```

しかし、クライアントが`http://example.com/items/bar`（存在しない`item_id` `"bar"`）をリクエストした場合、HTTPステータスコード404（"not found"エラー）と以下のJSONレスポンスが返されます:

```JSON
{
  "detail": "Item not found"
}
```

!!! tip "豆知識"
    `HTTPException`を発生させる際には、`str`だけでなく、JSONに変換できる任意の値を`detail`パラメータとして渡すことができます。

    `dist`や`list`などを渡すことができます。