Điều này cũng có nghĩa là trong Python 3.10, bạn có thể sử dụng `Something | None`:

//// tab | Python 3.10+

```Python hl_lines="1"
{!> ../../docs_src/python_types/tutorial009_py310.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="1  4"
{!> ../../docs_src/python_types/tutorial009.py!}
```

////

//// tab | Python 3.8+ alternative

```Python hl_lines="1  4"

**FastAPI** 知道在每种情况下该做什么以及如何复用同一对象，因此所有后台任务被合并在一起并且随后在后台运行：

//// tab | Python 3.10+

```Python hl_lines="13  15  22  25"
{!> ../../docs_src/background_tasks/tutorial002_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="13  15  22  25"
{!> ../../docs_src/background_tasks/tutorial002_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="14  16  23  26"

## `main.py` erstellen

Kopieren Sie das Beispiel in eine Datei `main.py`:

//// tab | Python 3.9+

```Python
{!> ../../docs_src/security/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python
{!> ../../docs_src/security/tutorial001_an.py!}
```

////

//// tab | Python 3.8+ nicht annotiert

/// tip | "Tipp"

Bevorzugen Sie die `Annotated`-Version, falls möglich.

//// tab | Uvicorn

<div class="termy">

```console
$ uvicorn main:app --host 0.0.0.0 --port 80

<span style="color: green;">INFO</span>:     Uvicorn running on http://0.0.0.0:80 (Press CTRL+C to quit)
```

</div>

////

//// tab | Hypercorn

<div class="termy">

```console
$ hypercorn main:app --bind 0.0.0.0:80

有个 `GET` 操作会返回错误。

有个 `POST` 操作会返回一些错误。

所有*路径操作* 都需要一个`X-Token` 头。

//// tab | Python 3.10+

```Python
{!> ../../docs_src/app_testing/app_b_an_py310/main.py!}
```

////

//// tab | Python 3.9+

```Python
{!> ../../docs_src/app_testing/app_b_an_py39/main.py!}
```

////

//// tab | Python 3.8+

```Python
{!> ../../docs_src/app_testing/app_b_an/main.py!}
```

Ambas as *operações de rotas* requerem um cabeçalho `X-Token`.

//// tab | Python 3.10+

```Python
{!> ../../docs_src/app_testing/app_b_an_py310/main.py!}
```

////

//// tab | Python 3.9+

```Python
{!> ../../docs_src/app_testing/app_b_an_py39/main.py!}
```

////

//// tab | Python 3.8+

```Python
{!> ../../docs_src/app_testing/app_b_an/main.py!}
```

//// tab | Python 3.9+

```Python hl_lines="6  14  22"
{!> ../../docs_src/dependencies/tutorial008_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="5  13  21"
{!> ../../docs_src/dependencies/tutorial008_an.py!}
```

////

//// tab | Python 3.8+ nicht annotiert

/// tip | "Tipp"

这不是 **FastAPI** 的问题，而是 HTTP 协议的规定。

///

## 可选文件上传

您可以通过使用标准类型注解并将 None 作为默认值的方式将一个文件参数设为可选:

//// tab | Python 3.9+

```Python hl_lines="7  14"
{!> ../../docs_src/request_files/tutorial001_02_py310.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="9  17"
{!> ../../docs_src/request_files/tutorial001_02.py!}
```

////

Both *path operations* require an `X-Token` header.

//// tab | Python 3.10+

```Python
{!> ../../docs_src/app_testing/app_b_an_py310/main.py!}
```

////

//// tab | Python 3.9+

```Python
{!> ../../docs_src/app_testing/app_b_an_py39/main.py!}
```

////

//// tab | Python 3.8+

```Python
{!> ../../docs_src/app_testing/app_b_an/main.py!}
```

### 主应用程序文件

现在我们创建一个依赖项，返回一个新的 `config.Settings()`。

//// tab | Python 3.9+

```Python hl_lines="6  12-13"
{!> ../../docs_src/settings/app02_an_py39/main.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="6  12-13"
{!> ../../docs_src/settings/app02_an/main.py!}
```

////

//// tab | Python 3.8+ 非注解版本

/// tip

如果可能，请尽量使用 `Annotated` 版本。

///