这段代码声明了类型为 `str` 的可选查询参数 `q`，然后返回这个查询参数。

这个函数很简单（不过也没什么用），但却有助于让我们专注于了解子依赖项的工作方式。

### 第二层依赖项

接下来，创建另一个依赖项函数，并同时用该依赖项自身再声明一个依赖项（所以这也是一个「依赖项」）：

{* ../../docs_src/dependencies/tutorial005.py hl[13] *}

这里重点说明一下声明的参数：

* 尽管该函数自身是依赖项，但还声明了另一个依赖项（它「依赖」于其他对象）
    * 该函数依赖 `query_extractor`, 并把 `query_extractor` 的返回值赋给参数 `q`
* 同时，该函数还声明了类型是 `str` 的可选 cookie（`last_query`）
    * 用户未提供查询参数 `q` 时，则使用上次使用后保存在 cookie 中的查询

pkg debug/elf, const STB_LOOS = 10
pkg debug/elf, const STB_LOPROC = 13
pkg debug/elf, const STB_WEAK = 2
pkg debug/elf, const STT_COMMON = 5
pkg debug/elf, const STT_FILE = 4
pkg debug/elf, const STT_FUNC = 2
pkg debug/elf, const STT_HIOS = 12
pkg debug/elf, const STT_HIPROC = 15
pkg debug/elf, const STT_LOOS = 10
pkg debug/elf, const STT_LOPROC = 13
pkg debug/elf, const STT_NOTYPE = 0
pkg debug/elf, const STT_OBJECT = 1

Por ejemplo, podrías tener un archivo `config.py` con:

{* ../../docs_src/settings/app01_py39/config.py *}

Y luego usarlo en un archivo `main.py`:

{* ../../docs_src/settings/app01_py39/main.py hl[3,11:13] *}

/// tip | Consejo

También necesitarías un archivo `__init__.py` como viste en [Aplicaciones Más Grandes - Múltiples Archivos](../tutorial/bigger-applications.md){.internal-link target=_blank}.

///

            (byte) 13, (byte) 5, (byte) 60, (byte) 52, (byte) 44, (byte) 36, (byte) 28, (byte) 20, (byte) 12, (byte) 4, (byte) 27,
            (byte) 19, (byte) 11, (byte) 3 };
    private static int[] totrot = { 1, 2, 4, 6, 8, 10, 12, 14, 15, 17, 19, 21, 23, 25, 27, 28 };

So, `0.5` would be a valid value. But `0.0` or `0` would not.

And the same for <abbr title="less than"><code>lt</code></abbr>.

{* ../../docs_src/path_params_numeric_validations/tutorial006_an_py39.py hl[13] *}

## Recap { #recap }

pkg debug/pe, const IMAGE_SUBSYSTEM_EFI_BOOT_SERVICE_DRIVER = 11
pkg debug/pe, const IMAGE_SUBSYSTEM_EFI_BOOT_SERVICE_DRIVER ideal-int
pkg debug/pe, const IMAGE_SUBSYSTEM_EFI_ROM = 13
pkg debug/pe, const IMAGE_SUBSYSTEM_EFI_ROM ideal-int
pkg debug/pe, const IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER = 12
pkg debug/pe, const IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER ideal-int
pkg debug/pe, const IMAGE_SUBSYSTEM_NATIVE = 1

For example, you could have a file `config.py` with:

{* ../../docs_src/settings/app01_py39/config.py *}

And then use it in a file `main.py`:

{* ../../docs_src/settings/app01_py39/main.py hl[3,11:13] *}

/// tip

You would also need a file `__init__.py` as you saw in [Bigger Applications - Multiple Files](../tutorial/bigger-applications.md){.internal-link target=_blank}.

///

      switch (bb.remaining()) {
        case 15:
          k2 ^= (long) toUnsignedInt(bb.get(14)) << 48; // fall through
        case 14:
          k2 ^= (long) toUnsignedInt(bb.get(13)) << 40; // fall through
        case 13:
          k2 ^= (long) toUnsignedInt(bb.get(12)) << 32; // fall through
        case 12:
          k2 ^= (long) toUnsignedInt(bb.get(11)) << 24; // fall through
        case 11:

    number of other development tools for reporting or the build
    process.
  </description>
  <url>http://maven.apache.org/</url>
  <inceptionYear>2001</inceptionYear>
  <properties>
    <classWorldsVersion>1.3</classWorldsVersion>
    <commonsCliVersion>1.0</commonsCliVersion>
    <!--

    Do not update this, Doxia will be decoupled completely from 3.x and someone can

Por ejemplo, podrías añadir un custom header `X-Process-Time` que contenga el tiempo en segundos que tomó procesar la request y generar una response:

{* ../../docs_src/middleware/tutorial001_py39.py hl[10,12:13] *}

/// tip | Consejo