}

        in 3..4 -> {
          source.readData(data)
        }

        in 5..7 -> {
          data.writeByte('\n'.code) // 'data' on a line of its own.
        }

        in 8..9 -> {
          id = source.readUtf8LineStrict().takeIf { it.isNotEmpty() }
        }

        in 10..12 -> {
          id = null // 'id' on a line of its own.
        }

        in 13..14 -> {

## Primeira dependência "dependable" { #first-dependency-dependable }

Você pode criar uma primeira dependência ("dependable") dessa forma:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

Esse código declara um parâmetro de consulta opcional, `q`, com o tipo `str`, e então retorna esse parâmetro.

Isso é bastante simples (e não muito útil), mas irá nos ajudar a focar em como as subdependências funcionam.

# 子依赖项

FastAPI 支持创建含**子依赖项**的依赖项。

并且，可以按需声明任意**深度**的子依赖项嵌套层级。

**FastAPI** 负责处理解析不同深度的子依赖项。

### 第一层依赖项

下列代码创建了第一层依赖项：

{* ../../docs_src/dependencies/tutorial005.py hl[8:9] *}

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：

```
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            35:ac:60:46:ad:8d:de:18:dc:0b:f6:98:14:ee:89:e8
        Signature Algorithm: ED25519
        Issuer: CN = consoleAdmin
        Validity
            Not Before: Jul 19 15:08:44 2021 GMT
            Not After : Aug 18 15:08:44 2021 GMT
        Subject: CN = consoleAdmin

    - [Client Binaries](#client-binaries-5)
    - [Server Binaries](#server-binaries-5)
    - [Node Binaries](#node-binaries-5)
  - [Changelog since v1.8.9](#changelog-since-v189)
    - [Other notable changes](#other-notable-changes-5)
- [v1.8.9](#v189)
  - [Downloads for v1.8.9](#downloads-for-v189)
    - [Client Binaries](#client-binaries-6)
    - [Server Binaries](#server-binaries-6)
    - [Node Binaries](#node-binaries-6)

Сначала сосредоточимся на зависимости.

Это просто функция, которая может принимать те же параметры, что и *функция обработки пути*:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

И всё.

**2 строки.**

И она имеет ту же форму и структуру, что и все ваши *функции обработки пути*.

Можно думать о ней как о *функции обработки пути* без «декоратора» (без `@app.get("/some-path")`).

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

	_ = x[ErrMissingFields-83]
	_ = x[ErrMissingCredTag-84]
	_ = x[ErrCredMalformed-85]
	_ = x[ErrInvalidRegion-86]
	_ = x[ErrInvalidServiceS3-87]
	_ = x[ErrInvalidServiceSTS-88]
	_ = x[ErrInvalidRequestVersion-89]
	_ = x[ErrMissingSignTag-90]
	_ = x[ErrMissingSignHeadersTag-91]
	_ = x[ErrMalformedDate-92]
	_ = x[ErrMalformedPresignedDate-93]
	_ = x[ErrMalformedCredentialDate-94]
	_ = x[ErrMalformedExpires-95]

Primero enfoquémonos en la dependencia.

Es solo una función que puede tomar todos los mismos parámetros que una *path operation function* puede tomar:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

Eso es todo.

**2 líneas**.

Y tiene la misma forma y estructura que todas tus *path operation functions*.

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