例如，您可以使用这种方式创建一个数据库会话，并在完成后关闭它。

在发送响应之前，只会执行 `yield` 语句及之前的代码：

```Python hl_lines="2-4"
{!../../../docs_src/dependencies/tutorial007.py!}
```

生成的值会注入到*路径操作*和其他依赖项中：

```Python hl_lines="4"
{!../../../docs_src/dependencies/tutorial007.py!}
```

"yield"语句后面的代码会在发送响应后执行：：

```Python hl_lines="5-6"
{!../../../docs_src/dependencies/tutorial007.py!}
```

!!! tip "提示"

    您可以使用 `async` 或普通函数。

这里说的不是类本身（类本就是可调用项），而是类实例。

为此，需要声明 `__call__` 方法：

```Python hl_lines="10"
{!../../../docs_src/dependencies/tutorial011.py!}
```

本例中，**FastAPI**  使用 `__call__` 检查附加参数及子依赖项，稍后，还要调用它向*路径操作函数*传递值。

## 参数化实例

接下来，使用 `__init__` 声明用于**参数化**依赖项的实例参数：

```Python hl_lines="7"
{!../../../docs_src/dependencies/tutorial011.py!}
```

本例中，**FastAPI** 不使用 `__init__`，我们要直接在代码中使用。

## 创建实例

使用以下代码创建类实例：

👈, 👥 📣 👩‍🔬 `__call__`:

```Python hl_lines="10"
{!../../../docs_src/dependencies/tutorial011.py!}
```

👉 💼, 👉 `__call__` ⚫️❔ **FastAPI** 🔜 ⚙️ ✅ 🌖 🔢 & 🎧-🔗, & 👉 ⚫️❔ 🔜 🤙 🚶‍♀️ 💲 🔢 👆 *➡ 🛠️ 🔢* ⏪.

## 🔗 👐

& 🔜, 👥 💪 ⚙️ `__init__` 📣 🔢 👐 👈 👥 💪 ⚙️ "🔗" 🔗:

```Python hl_lines="7"
{!../../../docs_src/dependencies/tutorial011.py!}
```

Nils Lindemann <******@****.***> 1711829852 +0100

LeeeeT <******@****.***> 1680341164 +0300

jaystone776 <******@****.***> 1711838753 +0800

    {!> ../../../docs_src/dependencies/tutorial008_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="17-18  25-26"
    {!> ../../../docs_src/dependencies/tutorial008_an.py!}
    ```

=== "Python 3.8+ nicht annotiert"

    !!! tip "Tipp"
        Bevorzugen Sie die `Annotated`-Version, falls möglich.

    ```Python hl_lines="16-17  24-25"
    {!> ../../../docs_src/dependencies/tutorial008.py!}

=== "Python 3.10+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/dependencies/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="11"
    {!> ../../../docs_src/dependencies/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/dependencies/tutorial001_an.py!}
    ```

=== "Python 3.10+ nicht annotiert"

```Python hl_lines="2-4"
{!../../../docs_src/dependencies/tutorial007.py!}
```

The yielded value is what is injected into *path operations* and other dependencies:

```Python hl_lines="4"
{!../../../docs_src/dependencies/tutorial007.py!}
```

The code following the `yield` statement is executed after the response has been delivered:

```Python hl_lines="5-6"
{!../../../docs_src/dependencies/tutorial007.py!}
```

!!! tip

    ```

=== "Python 3.8+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/dependencies/tutorial001_an.py!}
    ```

=== "Python 3.10+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="7"
    {!> ../../../docs_src/dependencies/tutorial001_py310.py!}
    ```

=== "Python 3.8+ non-Annotated"