!!! tip
    The `shutdown` would happen when you are **stopping** the application.

    Maybe you need to start a new version, or you just got tired of running it. 🤷

### Lifespan function

The first thing to notice, is that we are defining an async function with `yield`. This is very similar to Dependencies with `yield`.

```Python hl_lines="14-19"
{!../../../docs_src/events/tutorial003.py!}
```

<img src="/img/tutorial/extending-openapi/image03.png">

## Change the Theme

The same way you could set the syntax highlighting theme with the key `"syntaxHighlight.theme"` (notice that it has a dot in the middle):

```Python hl_lines="3"
{!../../../docs_src/configure_swagger_ui/tutorial002.py!}
```

That configuration would change the syntax highlighting color theme:

!!! tip
    Notice that the values you return are SQLAlchemy models, or lists of SQLAlchemy models.

    But as all the *path operations* have a `response_model` with Pydantic *models* / schemas using `orm_mode`, the data declared in your Pydantic models will be extracted from them and returned to the client, with all the normal filtering and validation.

!!! tip

```Python
something()
```

or

```Python
something(some_argument, some_keyword_argument="foo")
```

then it is a "callable".

## Classes as dependencies

You might notice that to create an instance of a Python class, you use that same syntax.

For example:

```Python
class Cat:
    def __init__(self, name: str):
        self.name = name


fluffy = Cat(name="Mr Fluffy")

```

</div>

这个命令会打开浏览器并自动验证身份。

## 使用 Deta 部署

接下来，使用 Deta CLI 部署应用：

<div class="termy">

```console
$ deta new

Successfully created a new micro

// Notice the "endpoint" 🔍

{
    "name": "fastapideta",
    "runtime": "python3.7",
    "endpoint": "https://qltnci.deta.dev",
    "visor": "enabled",
    "http_auth": "enabled"
}

Adding dependencies...

```Python hl_lines="19-24  28"
{!../../../docs_src/additional_responses/tutorial002.py!}
```

!!! note
    Notice that you have to return the image using a `FileResponse` directly.

!!! info

## Dependencies with `yield` and `except`

If you catch an exception using `except` in a dependency with `yield` and you don't raise it again (or raise a new exception), FastAPI won't be able to notice there was an exception, the same way that would happen with regular Python:

=== "Python 3.9+"

    ```Python hl_lines="15-16"
    {!> ../../../docs_src/dependencies/tutorial008c_an_py39.py!}
    ```

### The config file

Coming from the previous example, your `config.py` file could look like:

```Python hl_lines="10"
{!../../../docs_src/settings/app02/config.py!}
```

Notice that now we don't create a default instance `settings = Settings()`.

### The main app file

Now we create a dependency that returns a new `config.Settings()`.

=== "Python 3.9+"

name: Notify Translations

on:
  pull_request_target:
    types:
      - labeled
      - closed
  workflow_dispatch:
    inputs:
      number:
        description: PR number
        required: true
      debug_enabled:
        description: 'Run the build with tmate debugging enabled (https://github.com/marketplace/actions/debugging-with-tmate)'
        required: false
        default: 'false'

jobs:
  notify-translations:

# Handling Errors

There are many situations in which you need to notify an error to a client that is using your API.

This client could be a browser with a frontend, a code from someone else, an IoT device, etc.

You could need to tell the client that:

* The client doesn't have enough privileges for that operation.
* The client doesn't have access to that resource.
* The item the client was trying to access doesn't exist.
* etc.