**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 }

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.

* [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.

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

/// tip

As Pydantic will serialize it in the **Rust** side, you will get much higher **performance** than if you don't declare a return type.

///

### Non-async *path operation functions* { #non-async-path-operation-functions }

If you declare the return type, FastAPI will use it to **validate** the data, **document** it in OpenAPI, **filter** it, and **serialize** it using Pydantic.

/// tip

As Pydantic will serialize it in the **Rust** side, you will get much higher **performance** than if you don't declare a return type.

///

### Non-async *path operation functions* { #non-async-path-operation-functions }

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

如果你声明了返回类型，FastAPI 会用它来验证数据、在 OpenAPI 中生成文档、进行过滤，并使用 Pydantic 进行序列化。

/// tip | 提示

由于 Pydantic 会在 Rust 侧进行序列化，如果你声明了返回类型，将获得更高的性能。

///

### 非异步的*路径操作函数* { #non-async-path-operation-functions }

你也可以使用常规的 `def` 函数（不带 `async`），并以同样的方式使用 `yield`。

FastAPI 会确保其正确运行，不会阻塞事件循环。