Keep in mind that the server (Uvicorn) won't use that `root_path` for anything else than passing it to the app.

But if you go with your browser to <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000/app</a> you will see the normal response:

```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

This is different from using an `APIRouter` as a mounted application is completely independent. The OpenAPI and docs from your main application won't include anything from the mounted application, etc.

You can read more about this in the [Advanced User Guide](../advanced/index.md){.internal-link target=_blank}.

## Details

We annotate the function return type as `BaseUser`, but we are actually returning a `UserIn` instance.

The editor, mypy, and other tools won't complain about this because, in typing terms, `UserIn` is a subclass of `BaseUser`, which means it's a *valid* type when what is expected is anything that is a `BaseUser`.

### FastAPI Data Filtering

This will help us inside of the function with all the completion and type checks.

!!! tip
    You might remember that request bodies are also declared with Pydantic models.

    Here **FastAPI** won't get confused because you are using `Depends`.

!!! check
    The way this dependency system is designed allows us to have different dependencies (different "dependables") that all return a `User` model.

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

</div>

as Uvicorn by default will use the port `8000`, the documentation on port `8008` won't clash.

### Translations

Help with translations is VERY MUCH appreciated! And it can't be done without the help from the community. 🌎 🚀

Here are the steps to help with translations.

* 🌐 Add Korean translation for `docs/ko/docs/tutorial/path-operation-configuration.md`. PR [#3639](https://github.com/tiangolo/fastapi/pull/3639) by [@jungsu-kwon](https://github.com/jungsu-kwon).
* 🌐 Modify the description of `zh` - Traditional Chinese. PR [#10889](https://github.com/tiangolo/fastapi/pull/10889) by [@cherinyy](https://github.com/cherinyy).

It would also mean that if you get data from the `Request` object directly (for example, read the body) it won't be validated, converted or documented (with OpenAPI, for the automatic API user interface) by FastAPI.

```Python
say_hi(name=None)  # This works, None is valid 🎉
```

The good news is, once you are on Python 3.10 you won't have to worry about that, as you will be able to simply use `|` to define unions of types:

```Python hl_lines="1  4"
{!../../../docs_src/python_types/tutorial009c_py310.py!}
```

And then you won't have to worry about names like `Optional` and `Union`. 😎

#### Generic types

But you cannot convert from the gibberish back to the password.

### Why use password hashing

If your database is stolen, the thief won't have your users' plaintext passwords, only the hashes.

So, the thief won't be able to try to use that password in another system (as many users use the same password everywhere, this would be dangerous).

## Install `passlib`

But if your connection to the server is lost, the **running process** will probably die.

And if the server is restarted (for example after updates, or migrations from the cloud provider) you probably **won't notice it**. And because of that, you won't even know that you have to restart the process manually. So, your API will just stay dead. 😱

### Run Automatically on Startup