Sie können `async`hrone oder reguläre Funktionen verwenden.

    **FastAPI** wird bei jeder das Richtige tun, so wie auch bei normalen Abhängigkeiten.

## Eine Abhängigkeit mit `yield` und `try`.

Wenn Sie einen `try`-Block in einer Abhängigkeit mit `yield` verwenden, empfangen Sie alle Exceptions, die bei Verwendung der Abhängigkeit geworfen wurden.

### Path fonksiyonu

"async def" yerine normal "def" ile bir *yol işlem işlevi* bildirdiğinizde, doğrudan çağrılmak yerine (sunucuyu bloke edeceğinden) daha sonra beklenen harici bir iş parçacığı havuzunda çalıştırılır.

jieba==0.42.1
# For image processing by Material for MkDocs
pillow==10.3.0
# For image processing by Material for MkDocs
cairosvg==2.7.0
mkdocstrings[python]==0.24.3
griffe-typingdoc==0.2.2
# For griffe, it formats with black
black==24.3.0

{!../../../docs_src/custom_response/tutorial008.py!}
```

1. This is the generator function. It's a "generator function" because it contains `yield` statements inside.
2. By using a `with` block, we make sure that the file-like object is closed after the generator function is done. So, after it finishes sending the response.

### Path operation functions

When you declare a *path operation function* with normal `def` instead of `async def`, it is run in an external threadpool that is then awaited, instead of being called directly (as it would block the server).

<a href="https://github.com/deepset-ai/haystack/" target="_blank" title="Build powerful search from composable, open source building blocks"><img src="https://fastapi.tiangolo.com/img/sponsors/haystack-fastapi.svg"></a>
<a href="https://databento.com/" target="_blank" title="Pay as you go for market data"><img src="https://fastapi.tiangolo.com/img/sponsors/databento.svg"></a>

    **FastAPI** uses them internally to achieve this.

## Dependencies with `yield` and `HTTPException`

You saw that you can use dependencies with `yield` and have `try` blocks that catch exceptions.

The same way, you could raise an `HTTPException` or similar in the exit code, after the `yield`.

!!! tip

```Python
async with lifespan(app):
    await do_stuff()
```

When you create a context manager or an async context manager like above, what it does is that, before entering the `with` block, it will execute the code before the `yield`, and after exiting the `with` block, it will execute the code after the `yield`.

In our code example above, we don't use it directly, but we pass it to FastAPI for it to use it.

    {!> ../../../docs_src/sql_databases/sql_app/main.py!}
    ```

!!! info
    We put the creation of the `SessionLocal()` and handling of the requests in a `try` block.

    And then we close it in the `finally` block.

    This way we make sure the database session is always closed after the request. Even if there was an exception while processing the request.

It is also built to work as a future reference.

So you can come back and see exactly what you need.

## Run the code

All the code blocks can be copied and used directly (they are actually tested Python files).

To run any of the examples, copy the code to a file `main.py`, and start `fastapi dev` with:

<div class="termy">

```console