## HTTPX

Even if your **FastAPI** application uses normal `def` functions instead of `async def`, it is still an `async` application underneath.

    So, you should declare it with `...` to mark it as required.

    Nevertheless, even if you declared it with `None` or set a default value, it would not affect anything, it would still be always required.

## Order the parameters as you need

!!! tip
    This is probably not as important or necessary if you use `Annotated`.

# Extra Data Types

Up to now, you have been using common data types, like:

* `int`
* `float`
* `str`
* `bool`

But you can also use more complex data types.

And you will still have the same features as seen up to now:

* Great editor support.
* Data conversion from incoming requests.
* Data conversion for response data.
* Data validation.
* Automatic annotation and documentation.

## Other data types

    But OAuth2 with scopes can be nicely integrated into your API (with OpenAPI) and your API docs.

    Nevertheless, you still enforce those scopes, or any other security/authorization requirement, however you need, in your code.

    In many cases, OAuth2 with scopes can be an overkill.

    But if you know you need it, or you are curious, keep reading.

!!! info
    OpenAPI 3.1.0 (used since FastAPI 0.99.0) added support for `examples`, which is part of the **JSON Schema** standard.

    Before that, it only supported the keyword `example` with a single example. That is still supported by OpenAPI 3.1.0, but is deprecated and is not part of the JSON Schema standard. So you are encouraged to migrate `example` to `examples`. 🤓

    You can read more at the end of this page.

* API usage monitoring systems
* response data injection systems
* etc.

## Simple and Powerful

Although the hierarchical dependency injection system is very simple to define and use, it's still very powerful.

You can define dependencies that in turn can define dependencies themselves.

By only using `BackgroundTasks` (and not `BackgroundTask`), it's then possible to use it as a *path operation function* parameter and have **FastAPI** handle the rest for you, just like when using the `Request` object directly.

It's still possible to use `BackgroundTask` alone in FastAPI, but you have to create the object in your code and return a Starlette `Response` including it.

    ```Python hl_lines="21"
    {!> ../../../docs_src/separate_openapi_schemas/tutorial001.py!}
    ```

...then because `description` has a default value, if you **don't return anything** for that field, it will still have that **default value**.

### Model for Output Response Data

    example: Annotated[
        Optional[Any],
        typing_deprecated(
            "Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, "
            "although still supported. Use examples instead."
        ),
    ] = None


# Ref: https://json-schema.org/draft/2020-12/json-schema-core.html#name-json-schema-documents
# A JSON Schema MUST be an object or a boolean.

```Python hl_lines="2  4"
{!../../../docs_src/custom_response/tutorial010.py!}
```

!!! tip
    You can still override `response_class` in *path operations* as before.

## Additional documentation