And the part after the `yield` will be executed **after** the application has finished.

### Async Context Manager

If you check, the function is decorated with an `@asynccontextmanager`.

That converts the function into something called an "**async context manager**".

```Python hl_lines="1  13"
{!../../../docs_src/events/tutorial003.py!}
```

But you still need to define what is the dependable, the callable that you pass as a parameter to `Depends()` or `Security()`.

There are multiple tools that you can use to create those dependables, and they get integrated into OpenAPI so they are shown in the automatic docs UI, they can be used by automatically generated clients and SDKs, etc.

You can import them from `fastapi.security`:

```python
from fastapi.security import (
    APIKeyCookie,

In the next chapters you will see how to add security to your API using those tools provided by **FastAPI**.

## Technical Details

The class `BackgroundTasks` comes directly from <a href="https://www.starlette.io/background/" class="external-link" target="_blank">`starlette.background`</a>.

It is imported/included directly into FastAPI so that you can import it from `fastapi` and avoid accidentally importing the alternative `BackgroundTask` (without the `s` at the end) from `starlette.background`.

{!../../../docs_src/path_operation_advanced_configuration/tutorial006.py!}
```

In this example, we didn't declare any Pydantic model. In fact, the request body is not even <abbr title="converted from some plain format, like bytes, into Python objects">parsed</abbr> as JSON, it is read directly as `bytes`, and the function `magic_data_reader()` would be in charge of parsing it in some way.

Nevertheless, we can declare the expected schema for the request body.