**FastAPI** provides the same `starlette.responses` as `fastapi.responses` just as a convenience for you, the developer. But most of the available responses come directly from Starlette.

///

## Returning a custom `Response` { #returning-a-custom-response }

However, they are now deprecated as you will now get better performance by using a [Response Model - Return Type](https://fastapi.tiangolo.com/tutorial/response-model/).

That way, Pydantic will serialize the data into JSON bytes on the Rust side, which will achieve better performance than these custom JSON responses.

To optimize performance when returning JSON data, use a return type or response model, that way Pydantic will handle the serialization to JSON on the Rust side, without going through Python. Read more in the docs for [Tutorial - Response Model - Return Type](../tutorial/response-model.md).

## Documentation Tags - OpenAPI { #documentation-tags-openapi }

* [Daphne](https://github.com/django/daphne): ASGI-сервер, створений для Django Channels.
* [Granian](https://github.com/emmett-framework/granian): Rust HTTP-сервер для Python-застосунків.
* [NGINX Unit](https://unit.nginx.org/howto/fastapi/): NGINX Unit - легке й універсальне середовище виконання вебзастосунків.

## レスポンス性能の最適化 - レスポンスモデル - 戻り値の型 { #optimize-response-performance-response-model-return-type }

JSON データを返す際の性能を最適化するには、戻り値の型またはレスポンスモデルを使用してください。そうすることで、Pydantic が Python を経由せずに Rust 側で JSON へのシリアライズを処理します。詳細は [チュートリアル - レスポンスモデル - 戻り値の型](../tutorial/response-model.md) を参照してください。

## ドキュメントのタグ - OpenAPI { #documentation-tags-openapi }

{* ../../docs_src/stream_json_lines/tutorial001_py310.py ln[1:24] hl[9:11,22] *}

반환 타입을 선언하면 FastAPI가 이를 사용해 데이터를 **검증**하고, OpenAPI에 **문서화**하고, **필터링**하고, Pydantic으로 **직렬화**합니다.

/// tip

Pydantic이 **Rust** 측에서 직렬화하므로, 반환 타입을 선언하지 않았을 때보다 훨씬 높은 **성능**을 얻게 됩니다.

///

### 비동기 아님 *경로 처리 함수* { #non-async-path-operation-functions }

일반 `def` 함수(`async` 없이)도 사용할 수 있으며, 동일하게 `yield`를 사용할 수 있습니다.

* [Daphne](https://github.com/django/daphne): der für Django Channels entwickelte ASGI-Server.
* [Granian](https://github.com/emmett-framework/granian): Ein Rust HTTP-Server für Python-Anwendungen.
* [NGINX Unit](https://unit.nginx.org/howto/fastapi/): NGINX Unit ist eine leichte und vielseitige Laufzeitumgebung für Webanwendungen.

반환 타입을 `AsyncIterable[Item]`으로 선언하면 FastAPI가 이를 사용해 데이터를 Pydantic으로 **검증**, **문서화**, **직렬화**합니다.

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip | 팁

Pydantic이 **Rust** 쪽에서 직렬화하므로, 반환 타입을 선언하지 않았을 때보다 훨씬 더 높은 **성능**을 얻을 수 있습니다.

///

### 비 async *경로 처리 함수* { #non-async-path-operation-functions }

`async`가 없는 일반 `def` 함수도 사용할 수 있으며, 동일하게 `yield`를 사용할 수 있습니다.

  - type: input
    id: author-other-languages-experience
    attributes:
      label: "Other Languages Experience"
      description: "What other languages do you have experience with?"
      placeholder: "Go, Python, JS, Rust"
    validations:
      required: false

  - type: checkboxes
    id: related-idea
    attributes:
      label: "Related Idea"
      options:

```

**Important**: Return types or response models are what filter data ensuring no sensitive information is exposed. And they are used to serialize data with Pydantic (in Rust), this is the main idea that can increase response performance.

The return type doesn't have to be a Pydantic model, it could be a different type, like a list of integers, or a dict, etc.