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

The `lifespan` parameter of the `FastAPI` app takes an **async context manager**, so we can pass our new `lifespan` async context manager to it.

```Python hl_lines="22"
{!../../../docs_src/events/tutorial003.py!}
```

"_If anyone is looking to build a production Python API, I would highly recommend **FastAPI**. It is **beautifully designed**, **simple to use** and **highly scalable**, it has become a **key component** in our API first development strategy and is driving many automations and services such as our Virtual TAC Engineer._"

# Classes as Dependencies

Before diving deeper into the **Dependency Injection** system, let's upgrade the previous example.

## A `dict` from the previous example

In the previous example, we were returning a `dict` from our dependency ("dependable"):

=== "Python 3.10+"

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

=== "Python 3.9+"

    ```Python hl_lines="11"

Let's look at how we can make that work.

## pytest.mark.anyio

If we want to call asynchronous functions in our tests, our test functions have to be asynchronous. AnyIO provides a neat plugin for this, that allows us to specify that some test functions are to be called asynchronously.

## HTTPX

    If you need to enforce it, use `OAuth2PasswordRequestFormStrict` instead of `OAuth2PasswordRequestForm`.

* An optional `client_id` (we don't need it for our example).
* An optional `client_secret` (we don't need it for our example).

!!! info
    The `OAuth2PasswordRequestForm` is not a special class for **FastAPI** as is `OAuth2PasswordBearer`.

---

"_**Netflix** is pleased to announce the open-source release of our **crisis management** orchestration framework: **Dispatch**! [built with **FastAPI**]_"

---

<div style="text-align: left; direction: ltr;">"<strong>Netflix</strong> is pleased to announce the open-source release of our <strong>crisis management</strong> orchestration framework: <strong>Dispatch</strong>! [built with <strong>FastAPI</strong>]"</div>

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

In this case, **FastAPI** won't ever touch or care about `__init__`, we will use it directly in our code.

## Create an instance

We could create an instance of this class with:

=== "Python 3.9+"

    ```Python hl_lines="18"
    {!> ../../../docs_src/dependencies/tutorial011_an_py39.py!}
    ```

    ```Python hl_lines="15"
    {!> ../../../docs_src/dependencies/tutorial008d.py!}
    ```

Now the client will get the same *HTTP 500 Internal Server Error* response, but the server will have our custom `InternalError` in the logs. 😎

## Execution of dependencies with `yield`

For that, we will create a new dependency with `yield`, as explained before in the section about [Dependencies with `yield`](dependencies/dependencies-with-yield.md){.internal-link target=_blank}.

Our dependency will create a new SQLAlchemy `SessionLocal` that will be used in a single request, and then close it once the request is finished.

=== "Python 3.9+"

    ```Python hl_lines="13-18"