Quando a requisição contém dados inválidos, **FastAPI** internamente lança para o `RequestValidationError`.

Para sobrescrevê-lo, importe o `RequestValidationError` e use-o com o `@app.exception_handler(RequestValidationError)` para decorar o manipulador de exceções.

```Python hl_lines="2  14-16"
{!../../docs_src/handling_errors/tutorial004.py!}
```

Se você for ao `/items/foo`, em vez de receber o JSON padrão com o erro:

```JSON
{

```

////

Das war's schon.

**Zwei Zeilen**.

Und sie hat die gleiche Form und Struktur wie alle Ihre *Pfadoperation-Funktionen*.

Sie können sie sich als *Pfadoperation-Funktion* ohne den „Dekorator“ (ohne `@app.get("/some-path")`) vorstellen.

Und sie kann alles zurückgeben, was Sie möchten.

In diesem Fall erwartet diese Abhängigkeit:

* Einen optionalen Query-Parameter `q`, der ein `str` ist.

compilation to JavaScript, it cannot rely on the types to define validation, serialization and documentation at the same time. Due to this and some design decisions, to get validation, serialization and automatic schema generation, it's needed to add decorators in many places. So, it becomes quite verbose.

It can't handle nested models very well. So, if the JSON body in the request is a JSON object that has inner fields that in turn are nested JSON objects, it cannot be properly documented and...

我们还可以添加一个 `tags` 列表和额外的 `responses` 列表，这些参数将应用于此路由器中包含的所有*路径操作*。

我们可以添加一个 `dependencies` 列表，这些依赖项将被添加到路由器中的所有*路径操作*中，并将针对向它们发起的每个请求执行/解决。

/// tip

请注意，和[*路径操作装饰器*中的依赖项](dependencies/dependencies-in-path-operation-decorators.md){.internal-link target=_blank}很类似，没有值会被传递给你的*路径操作函数*。

///

最终结果是项目相关的路径现在为：

* `/items/`
* `/items/{item_id}`

...如我们所愿。

* 它们将被标记为仅包含单个字符串 `"items"` 的标签列表。

```Python
def get_settings():
    return Settings()
```

würden wir dieses Objekt für jeden Request erstellen und die `.env`-Datei für jeden Request lesen. ⚠️

Da wir jedoch den `@lru_cache`-Dekorator oben verwenden, wird das `Settings`-Objekt nur einmal erstellt, nämlich beim ersten Aufruf. ✔️

//// tab | Python 3.9+

```Python hl_lines="1  11"
{!> ../../docs_src/settings/app03_an_py39/main.py!}
```

## `Security` 👨‍🎨 `dependencies`

import org.eclipse.aether.named.providers.NoopNamedLockFactory;
import org.eclipse.aether.spi.artifact.ArtifactPredicateFactory;
import org.eclipse.aether.spi.artifact.decorator.ArtifactDecoratorFactory;
import org.eclipse.aether.spi.artifact.generator.ArtifactGeneratorFactory;
import org.eclipse.aether.spi.checksums.ProvidedChecksumsSource;
import org.eclipse.aether.spi.checksums.TrustedChecksumsSource;

**FastAPI** 的 `fastapi.security.oauth2` 里包含了所有 OAuth2 身份验证流工具。

## 装饰器 `dependencies` 中的 `Security`

The important thing is that by using standard Python types, in a single place (instead of adding more classes, decorators, etc), **FastAPI** will do a lot of the work for you.

/// info

import org.eclipse.aether.named.providers.NoopNamedLockFactory;
import org.eclipse.aether.spi.artifact.ArtifactPredicateFactory;
import org.eclipse.aether.spi.artifact.decorator.ArtifactDecoratorFactory;
import org.eclipse.aether.spi.artifact.generator.ArtifactGeneratorFactory;
import org.eclipse.aether.spi.checksums.ProvidedChecksumsSource;
import org.eclipse.aether.spi.checksums.TrustedChecksumsSource;