因為這些程式碼分別在應用開始接收請求**之前**與**完成**處理請求之後執行，所以涵蓋了整個應用的**生命週期**（「lifespan」這個詞稍後會很重要 😉）。

這對於為整個應用設定需要**共用**於多個請求的**資源**，以及在之後進行**清理**，非常有用。比如資料庫連線池、或載入一個共用的機器學習模型。

## 使用情境 { #use-case }

先從一個**使用情境**開始，然後看看如何用這個機制解決。

想像你有一些要用來處理請求的**機器學習模型**。🤖

同一組模型會在多個請求間共用，所以不是每個請求或每個使用者各有一個模型。

再想像一下，載入模型**需要一段時間**，因為它必須從**磁碟**讀取大量資料。所以你不想在每個請求都做一次。

///

變數 `oauth2_scheme` 是 `OAuth2PasswordBearer` 的實例，但同時它也是「可呼叫的」（callable）。

它可以這樣被呼叫：

```Python
oauth2_scheme(some, parameters)
```

因此它可以配合 `Depends` 使用。

### 如何使用 { #use-it }

現在你可以在相依性中傳入 `oauth2_scheme` 與 `Depends` 搭配。

{* ../../docs_src/security/tutorial001_an_py310.py hl[12] *}

此相依性會提供一個 `str`，指派給「路徑操作函式」的參數 `token`。

///

`oauth2_scheme` 变量是 `OAuth2PasswordBearer` 的一个实例，同时它也是“可调用”的。

可以像这样调用：

```Python
oauth2_scheme(some, parameters)
```

因此，它可以与 `Depends` 一起使用。

### 使用 { #use-it }

现在你可以通过 `Depends` 将 `oauth2_scheme` 作为依赖传入。

{* ../../docs_src/security/tutorial001_an_py310.py hl[12] *}

该依赖会提供一个 `str`，赋值给*路径操作函数*的参数 `token`。

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

warn(String); } org/apache/maven/wrapper/MavenWrapperMain.class package org.apache.maven.wrapper; public synchronized class MavenWrapperMain { public static final String DEFAULT_MAVEN_USER_HOME; public static final String MAVEN_USER_HOME_PROPERTY_KEY = maven.user.home; public static final String MAVEN_USER_HOME_ENV_KEY = MAVEN_USER_HOME; public static final String MVNW_VERBOSE = MVNW_VERBOSE; public static final String MVNW_USERNAME = MVNW_USERNAME; public static final String MVNW_PASSWORD = MVNW_PASSWORD;...

     *
     * @return the dialectRevision
     */
    public int getDialectRevision() {
        return this.dialectRevision;
    }

    /**
     * Gets the server GUID used for identification.
     *
     * @return the serverGuid
     */
    public byte[] getServerGuid() {
        return this.serverGuid;
    }

    /**
     * @return the selectedDialect
     */

 * sourceDominant, Map&lt;Object, Object&gt; context )</code> for each field of each model class</li>
 * <li><code>Object get<i>Classname</i>Key( <i>Classname</i> <i>classname</i> )</code>
 * for each class that is used in a list</li>
 * </ul>
 * Code is written like it could be generated, with default behaviour to be overridden when necessary.

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,