## An app with callbacks

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

## Um aplicativo com callbacks

Vamos ver tudo isso com um exemplo.

Imagine que você tem um aplicativo que permite criar faturas.

Essas faturas terão um `id`, `title` (opcional), `customer` e `total`.

O usuário da sua API (um desenvolvedor externo) criará uma fatura em sua API com uma solicitação POST.

Então sua API irá (vamos imaginar):

但表单包含文件时，编码为 `multipart/form-data`。使用了 `File`，**FastAPI** 就知道要从请求体的正确位置获取文件。

编码和表单字段详见 <a href="https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Methods/POST" class="external-link" target="_blank"><abbr title="Mozilla Developer Network">MDN</abbr> Web 文档的 <code>POST </code></a> 小节。

///

/// warning | "警告"

    command = invocation_results.get('command')
    command_type = invocation_results.get('command_type')

    case_attrib = attrib.copy()
    if command_type:
      command_type = command_type.title()
      case_name = f'{command_type} invocation {invocation_id}'
    else:
      case_name = f' Invocation {invocation_id}'
    case_attrib.update({'name': case_name,

 * factory classes like:
 *
 * <pre>
 * interface Book {...}
 * public class Books {
 *   public static Book hardcover(String title) {...}
 *   public static Book paperback(String title) {...}
 * }
 * </pre>
 *
 * <p>And all the created {@code Book} instances can be tested with:
 *
 * <pre>
 * new ClassSanityTester()
 *     .forAllPublicStaticMethods(Books.class)

// Entre no diretório do projeto
$ cd awesome-project
```

</div>

## Crie um ambiente virtual

Ao começar a trabalhar em um projeto Python **pela primeira vez**, crie um ambiente virtual **<abbr title="existem outras opções, esta é uma diretriz simples">dentro do seu projeto</abbr>**.

/// tip | "Dica"

Você só precisa fazer isso **uma vez por projeto**, não toda vez que trabalhar.

///

//// tab | `venv`

# Зависимости

**FastAPI** имеет очень мощную и интуитивную систему **<abbr title="also known as components, resources, providers, services, injectables">Dependency Injection</abbr>**.

Она проектировалась таким образом, чтобы быть простой в использовании и облегчить любому разработчику интеграцию других компонентов с **FastAPI**.

## Что такое "Dependency Injection" (инъекция зависимости)

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      Contributor provides its Contributions) on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
      implied, including, without limitation, any warranties or conditions
      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
      PARTICULAR PURPOSE. You are solely responsible for determining the
      appropriateness of using or redistributing the Work and assume any