link: https://medium.com/@tiangolo
  - icon: fontawesome/solid/globe
    link: https://tiangolo.com
  alternate:
  - link: /
    name: en - English
  - link: /az/
    name: az - azərbaycan dili
  - link: /bn/
    name: bn - বাংলা
  - link: /de/
    name: de - Deutsch
  - link: /es/
    name: es - español
  - link: /fa/
    name: fa - فارسی
  - link: /fr/
    name: fr - français
  - link: /he/

## Learn about Guava

-   Our users' guide, [Guava Explained]
-   [A nice collection](https://www.tfnico.com/presentations/google-guava) of
    other helpful links

## Links

-   [GitHub project](https://github.com/google/guava)
-   [Issue tracker: Report a defect or feature request](https://github.com/google/guava/issues/new)

* Fix typo/link in External Links. PR [#1702](https://github.com/tiangolo/fastapi/pull/1702).
* Update handling of [External Links](https://fastapi.tiangolo.com/external-links/) to use a data file and allow translating the headers without becoming obsolete quickly when new links are added. PR [#https://github.com/tiangolo/fastapi/pull/1701](https://github.com/tiangolo/fastapi/pull/1701).

=== "Python 3.10+"

    ```Python hl_lines="68-69  82"
    {!> ../../../docs_src/websockets/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="68-69  82"
    {!> ../../../docs_src/websockets/tutorial002_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="69-70  83"
    {!> ../../../docs_src/websockets/tutorial002_an.py!}
    ```

=== "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"

<a href="https://github.com/containous/traefik/releases" class="external-link" target="_blank">Download Traefik</a>, it's a single binary, you can extract the compressed file and run it directly from the terminal.

Then create a file `traefik.toml` with:

```TOML hl_lines="3"
[entryPoints]
  [entryPoints.http]
    address = ":9999"

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!}
```

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip
    The `callback_url` query parameter uses a Pydantic <a href="https://docs.pydantic.dev/latest/concepts/types/#urls" class="external-link" target="_blank">URL</a> type.

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**.

If you run it and go to <a href="http://localhost:8000/v1/" class="external-link" target="_blank">http://localhost:8000/v1/</a> you will see the response from Flask:

* Automatic data model documentation with <a href="https://json-schema.org/" class="external-link" target="_blank"><strong>JSON Schema</strong></a> (as OpenAPI...