```Python hl_lines="2  6"
{!../../../docs_src/advanced_middleware/tutorial001.py!}
```

## `TrustedHostMiddleware`

Enforces that all incoming requests have a correctly set `Host` header, in order to guard against HTTP Host Header attacks.

```Python hl_lines="2  6-8"
{!../../../docs_src/advanced_middleware/tutorial002.py!}
```

The following arguments are supported:

You will see the automatic API docs for the sub-application, including only its own _path operations_, all under the correct sub-path prefix `/subapi`:

<img src="/img/tutorial/sub-applications/image02.png">

If you try interacting with any of the two user interfaces, they will work correctly, because the browser will be able to talk to each specific app or sub-app.

### Technical Details: `root_path`

                                    "normal": {
                                        "summary": "A normal example",
                                        "description": "A **normal** item works correctly.",
                                        "value": {
                                            "name": "Foo",
                                            "description": "A very nice Item",

* 🚮 🎚 📄 `UserInDB` 🏷.

🏗 🔢 👈 🕴 💡 🤚 👆 👩‍💻 ⚪️➡️ `username` (⚖️ 🙆 🎏 🔢) 🔬 👆 *➡ 🛠️ 🔢*, 👆 💪 🌖 💪 🏤-⚙️ ⚫️ 💗 🍕 &amp; 🚮 <abbr title="Automated test, written in code, that checks if another piece of code is working correctly.">⚒ 💯</abbr> ⚫️:

```Python hl_lines="36-42"
{!../../../docs_src/nosql_databases/tutorial001.py!}
```

### Ⓜ-🎻

Import `Enum` and create a sub-class that inherits from `str` and from `Enum`.

By inheriting from `str` the API docs will be able to know that the values must be of type `string` and will be able to render correctly.

Then create class attributes with fixed values, which will be the available valid values:

```Python hl_lines="1  6-9"
{!../../../docs_src/path_params/tutorial005.py!}
```

!!! info

### Generate a TypeScript Client with Tags

If you generate a client for a FastAPI app using tags, it will normally also separate the client code based on the tags.

This way you will be able to have things ordered and grouped correctly for the client code:

<img src="/img/tutorial/generate-clients/image06.png">

In this case you have:

* `ItemsService`
* `UsersService`

### Client Method Names

<img src="/img/tutorial/behind-a-proxy/image01.png">

But if we access the docs UI at the "official" URL using the proxy with port `9999`, at `/api/v1/docs`, it works correctly! 🎉

You can check it at <a href="http://127.0.0.1:9999/api/v1/docs" class="external-link" target="_blank">http://127.0.0.1:9999/api/v1/docs</a>:

<img src="/img/tutorial/behind-a-proxy/image02.png">

<div class="termy">

```console
$ bash scripts/format.sh
```

</div>

It will also auto-sort all your imports.

For it to sort them correctly, you need to have FastAPI installed locally in your environment, with the command in the section above using `-e`.

## Docs

```Python hl_lines="36-42"
{!../../../docs_src/nosql_databases/tutorial001.py!}
```

### f-strings

    It is equivalent to `set(["name", "description"])`.

#### Using `list`s instead of `set`s

If you forget to use a `set` and use a `list` or `tuple` instead, FastAPI will still convert it to a `set` and it will work correctly:

=== "Python 3.10+"

    ```Python hl_lines="29  35"
    {!> ../../../docs_src/response_model/tutorial006_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="31  37"