For example:

```Python hl_lines="4-7"
{!../../../docs_src/behind_a_proxy/tutorial003.py!}
```

Will generate an OpenAPI schema like:

```JSON hl_lines="5-7"
{
    "openapi": "3.1.0",
    // More stuff here
    "servers": [
        {
            "url": "/api/v1"
        },
        {

You could also define it as a normal function instead of `async def`:

```Python hl_lines="7"
{!../../../docs_src/first_steps/tutorial003.py!}
```

!!! note
    If you don't know the difference, check the [Async: *"In a hurry?"*](../async.md#in-a-hurry){.internal-link target=_blank}.

### Step 5: return the content

```Python hl_lines="8"
{!../../../docs_src/first_steps/tutorial001.py!}
```

The key updated docs are:

* Python Types Intro:

=== "Python 3.9+"

    ```Python hl_lines="1  11"
    {!> ../../../docs_src/settings/app03_an_py39/main.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="1  11"
    {!> ../../../docs_src/settings/app03_an/main.py!}
    ```

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="1  10"

## Using `WSGIMiddleware`

You need to import `WSGIMiddleware`.

Then wrap the WSGI (e.g. Flask) app with the middleware.

And then mount that under a path.

```Python hl_lines="2-3  23"
{!../../../docs_src/wsgi/tutorial001.py!}
```

## Check it

Now, every request under the path `/v1/` will be handled by the Flask application.

And the rest will be handled by **FastAPI**.

    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>Or use <code>async def</code>...</summary>

If your code uses `async` / `await`, use `async def`:

```Python hl_lines="9  14"
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")