## Umgebungsvariablen

/// tip | "Tipp"

Wenn Sie bereits wissen, was „Umgebungsvariablen“ sind und wie man sie verwendet, können Sie gerne mit dem nächsten Abschnitt weiter unten fortfahren.

///

 * systems and high-level APIs that provide autoescaping.
 * One Google-authored templating system available for external use is <a
 * href="https://developers.google.com/closure/templates/">Closure Templates</a>.
 *
 * <p>HTML escaping is particularly tricky: For example, <a
 * href="https://www.w3.org/TR/html4/types.html#h-6.2">some elements' text contents must not be HTML

* Sie können Metadaten aus der hochgeladenen Datei auslesen.
* Es hat eine <abbr title="dateiartig"><a href="https://docs.python.org/3/glossary.html#term-file-like-object" class="external-link" target="_blank">file-like</a></abbr> `async`hrone Schnittstelle.

* Você pode obter metadados do arquivo enviado.
* Ela possui uma interface <a href="https://docs.python.org/3/glossary.html#term-file-like-object" class="external-link" target="_blank">semelhante a arquivos</a> `async`.

# History, Design and Future

Some time ago, <a href="https://github.com/fastapi/fastapi/issues/3#issuecomment-454956920" class="external-link" target="_blank">a **FastAPI** user asked</a>:

> What’s the history of this project? It seems to have come from nowhere to awesome in a few weeks [...]

Here's a little bit of that history.

## Alternatives

# História, Design e Futuro

Há algum tempo, <a href="https://github.com/fastapi/fastapi/issues/3#issuecomment-454956920" class="external-link" target="_blank">um usuário **FastAPI** perguntou</a>:

> Qual é a história desse projeto? Parece que surgiu do nada e se tornou incrível em poucas semanas [...]

Aqui está um pouco dessa história.

## Alternativas

这部分文档在 `/docs` 下的 Swagger API 文档中显示，并且会告诉外部开发者如何构建*外部 API*。

本例没有实现回调本身（只是一行代码），只有文档部分。

/// tip | "提示"

实际的回调只是 HTTP 请求。

实现回调时，要使用 <a href="https://www.encode.io/httpx/" class="external-link" target="_blank">HTTPX</a> 或 <a href="https://requests.readthedocs.io/" class="external-link" target="_blank">Requests</a>。

///

## 编写回调文档代码

应用不执行这部分代码，只是用它来*记录 外部 API* 。

* Из загруженного файла можно получить метаданные.
* Он реализует <a href="https://docs.python.org/3/glossary.html#term-file-like-object" class="external-link" target="_blank">file-like</a> `async` интерфейс.

Und der Rest wird von **FastAPI** gehandhabt.

Wenn Sie das mit Uvicorn ausführen und auf <a href="http://localhost:8000/v1/" class="external-link" target="_blank">http://localhost:8000/v1/</a> gehen, sehen Sie die Response von Flask:

```txt
Hello, World from Flask!
```

E o resto será manipulado pelo **FastAPI**.

Se você rodar a aplicação e ir até <a href="http://localhost:8000/v1/" class="external-link" target="_blank">http://localhost:8000/v1/</a>, você verá o retorno do Flask:

```txt
Hello, World from Flask!
```

E se você for até <a href="http://localhost:8000/v2" class="external-link" target="_blank">http://localhost:8000/v2</a>, você verá o retorno do FastAPI: