---

If you just don't know, use normal `def`.

---

**Note**: You can mix `def` and `async def` in your *path operation functions* as much as you need and define each one using the best option for you. FastAPI will do the right thing with them.

Anyway, in any of the cases above, FastAPI will still work asynchronously and be extremely fast.

But by following the steps above, it will be able to do some performance optimizations.

# Extending OpenAPI

There are some cases where you might need to modify the generated OpenAPI schema.

In this section you will see how.

## The normal process

The normal (default) process, is as follows.

A `FastAPI` application (instance) has an `.openapi()` method that is expected to return the OpenAPI schema.

    </div>
  </div>
  <div id="announce-right" style="position: relative;">
    <div class="item">

    You can actually skip that extra header and it would still work.

    But it's provided here to be compliant with the specifications.

    Also, there might be tools that expect and use it (now or in the future) and that might be useful for you or your users, now or in the future.

    That's the benefit of standards...

## See it in action

```Python hl_lines="2  7"
{!../../../docs_src/custom_response/tutorial001.py!}
```

!!! tip
    It's possible that `ORJSONResponse` might be a faster alternative.

### `RedirectResponse`

Returns an HTTP redirect. Uses a 307 status code (Temporary Redirect) by default.

You can return a `RedirectResponse` directly:

```Python hl_lines="2  9"

                    <mxGeometry x="755" y="290" width="300" height="80" as="geometry"/>
                </mxCell>
                <mxCell id="6" value="" style="rounded=0;whiteSpace=wrap;html=1;fontStyle=1;strokeWidth=4;fillColor=#dae8fc;strokeColor=#6c8ebf;" parent="1" vertex="1">
                    <mxGeometry x="1110" y="410" width="190" height="500" as="geometry"/>
                </mxCell>

                    <mxGeometry x="-60" y="-540" width="330" height="260" as="geometry"/>
                </mxCell>
                <mxCell id="6" value="" style="rounded=0;whiteSpace=wrap;html=1;fontStyle=1;strokeWidth=4;fillColor=#dae8fc;strokeColor=#6c8ebf;" parent="1" vertex="1">
                    <mxGeometry x="495" y="320" width="355" height="440" as="geometry"/>
                </mxCell>

It will have a property `scopes` with a list containing all the scopes required by itself and all the dependencies that use this as a sub-dependency. That means, all the "dependants"... this might sound confusing, it is explained again later below.

                <mxCell id="1" parent="0"/>
                <mxCell id="2" value="" style="rounded=0;whiteSpace=wrap;html=1;fontStyle=1;strokeWidth=4;" parent="1" vertex="1">
                    <mxGeometry x="450" y="-50" width="820" height="970" as="geometry"/>
                </mxCell>

We are going to override the internal parts of Peewee that use `threading.local` and replace them with `contextvars`, with the corresponding updates.

This might seem a bit complex (and it actually is), you don't really need to completely understand how it works to use it.

We will create a `PeeweeConnectionState`:

```Python hl_lines="10-19"