opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> tasks: Handle exceptions in the background task code
    end
```

/// info | 说明

只会向客户端发送 **一次响应** ，可能是一个错误响应，也可能是来自 *路由函数* 的响应。

在发送了其中一个响应之后，就无法再发送其他响应了。

///

/// tip | 提示

```

你通常会使用`pip`安装这些依赖项：

<div class="termy">

```console
$ pip install -r requirements.txt
---> 100%
Successfully installed fastapi pydantic uvicorn
```

</div>

/// info

还有其他文件格式和工具来定义和安装依赖项。

 我将在下面的部分中向你展示一个使用 Poetry 的示例。 👇

///

### 创建 **FastAPI** 代码

* 创建`app`目录并进入。
* 创建一个空文件`__init__.py`。
* 创建一个 `main.py` 文件：



```Python

# 仮想環境

Pythonプロジェクトの作業では、**仮想環境**（または類似の仕組み）を使用し、プロジェクトごとにインストールするパッケージを分離するべきでしょう。

/// info | 情報

もし、仮想環境の概要や作成方法、使用方法について既にご存知なら、このセクションをスキップすることができます。🤓

///

/// tip | 豆知識

**仮想環境**は、**環境変数**とは異なります。

**環境変数**は、プログラムが使用できるシステム内の変数です。

**仮想環境**は、ファイルをまとめたディレクトリのことです。

///

/// info | 情報
このページでは、**仮想環境**の使用方法と、そのはたらきについて説明します。

sleep 2 ; # 1 second intervals between attempts $MC_COMMAND ; STATUS=$? ; done ; set -e ; # reset `e` as active return 0 } # checkUserExists ($username) # Check if the user exists, by using the exit code of `mc admin user info` checkUserExists() { USER=$1 CMD=$(${MC} admin user info myminio $USER > /dev/null 2>&1) return $? } # createUser ($username, $password, $policy) createUser() { USER=$1 PASS=$2 POLICY=$3 # Create the user if it does not exist if ! checkUserExists $USER ; then echo "Creating user...

sleep 2 ; # 1 second intervals between attempts $MC_COMMAND ; STATUS=$? ; done ; set -e ; # reset `e` as active return 0 } # checkUserExists ($username) # Check if the user exists, by using the exit code of `mc admin user info` checkUserExists() { USER=$1 CMD=$(${MC} admin user info myminio $USER > /dev/null 2>&1) return $? } # createUser ($username, $password, $policy) createUser() { USER=$1 PASS=$2 POLICY=$3 # Create the user if it does not exist if ! checkUserExists $USER ; then echo "Creating user...

sleep 2 ; # 1 second intervals between attempts $MC_COMMAND ; STATUS=$? ; done ; set -e ; # reset `e` as active return 0 } # checkUserExists ($username) # Check if the user exists, by using the exit code of `mc admin user info` checkUserExists() { USER=$1 CMD=$(${MC} admin user info myminio $USER > /dev/null 2>&1) return $? } # createUser ($username, $password, $policy) createUser() { USER=$1 PASS=$2 POLICY=$3 # Create the user if it does not exist if ! checkUserExists $USER ; then echo "Creating user...

sleep 2 ; # 1 second intervals between attempts $MC_COMMAND ; STATUS=$? ; done ; set -e ; # reset `e` as active return 0 } # checkUserExists ($username) # Check if the user exists, by using the exit code of `mc admin user info` checkUserExists() { USER=$1 CMD=$(${MC} admin user info myminio $USER > /dev/null 2>&1) return $? } # createUser ($username, $password, $policy) createUser() { USER=$1 PASS=$2 POLICY=$3 # Create the user if it does not exist if ! checkUserExists $USER ; then echo "Creating user...

sleep 2 ; # 1 second intervals between attempts $MC_COMMAND ; STATUS=$? ; done ; set -e ; # reset `e` as active return 0 } # checkUserExists ($username) # Check if the user exists, by using the exit code of `mc admin user info` checkUserExists() { USER=$1 CMD=$(${MC} admin user info myminio $USER > /dev/null 2>&1) return $? } # createUser ($username, $password, $policy) createUser() { USER=$1 PASS=$2 POLICY=$3 # Create the user if it does not exist if ! checkUserExists $USER ; then echo "Creating user...

sleep 2 ; # 1 second intervals between attempts $MC_COMMAND ; STATUS=$? ; done ; set -e ; # reset `e` as active return 0 } # checkUserExists ($username) # Check if the user exists, by using the exit code of `mc admin user info` checkUserExists() { USER=$1 CMD=$(${MC} admin user info myminio $USER > /dev/null 2>&1) return $? } # createUser ($username, $password, $policy) createUser() { USER=$1 PASS=$2 POLICY=$3 # Create the user if it does not exist if ! checkUserExists $USER ; then echo "Creating user...

    opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> tasks: Handle exceptions in the background task code
    end
```

/// info | 정보

클라이언트에 **하나의 응답** 만 전송됩니다. 이는 오류 응답 중 하나일 수도 있고,*경로 작업*에서 생성된 응답일 수도 있습니다.

이러한 응답 중 하나가 전송된 후에는 다른 응답을 보낼 수 없습니다.

///

/// tip | 팁