### FastAPI Data Filtering

Now, for FastAPI, it will see the return type and make sure that what you return includes **only** the fields that are declared in the type.

If you install Typer CLI, you can install completion with:

<div class="termy">

```console
$ typer --install-completion

zsh completion installed in /home/user/.bashrc.
Completion will take effect once you restart the terminal.
```

</div>

### Docs Structure

The documentation uses <a href="https://www.mkdocs.org/" class="external-link" target="_blank">MkDocs</a>.

If you are not familiar with the `UserInDB(**result.value)`, <a href="https://docs.python.org/3/glossary.html#term-argument" class="external-link" target="_blank">it is using `dict` "unpacking"</a>.

It will take the `dict` at `result.value`, and take each of its keys and values and pass them as key-values to `UserInDB` as keyword arguments.

So, if the `dict` contains:

```Python
{
    "username": "johndoe",

The security and dependency injection stuff is written once.

And you can make it as complex as you want. And still, have it written only once, in a single place. With all the flexibility.

But you can have thousands of endpoints (*path operations*) using the same security system.

And all of them (or any portion of them that you want) can take the advantage of re-using these dependencies or any other dependencies you create.

🚥 👆 ❎ 🏎 ✳, 👆 💪 ❎ 🛠️ ⏮️:

<div class="termy">

```console
$ typer --install-completion

zsh completion installed in /home/user/.bashrc.
Completion will take effect once you restart the terminal.
```

</div>

### 📱 &amp; 🩺 🎏 🕰

🚥 👆 🏃 🖼 ⏮️, ✅:

<div class="termy">

```console
$ uvicorn tutorial001:app --reload

These examples run the server program (e.g Uvicorn), starting **a single process**, listening on all the IPs (`0.0.0.0`) on a predefined port (e.g. `80`).

This is the basic idea. But you will probably want to take care of some additional things, like:

* Security - HTTPS
* Running on startup
* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting

### Technical Details: `root_path`

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

That way, the sub-application will know to use that path prefix for the docs UI.

This schema definition includes your API paths, the possible parameters they take, etc.

#### Data "schema"

The term "schema" might also refer to the shape of some data, like a JSON content.

In that case, it would mean the JSON attributes, and data types they have, etc.

The only thing the function returned by `GzipRequest.get_route_handler` does differently is convert the `Request` to a `GzipRequest`.

Doing this, our `GzipRequest` will take care of decompressing the data (if necessary) before passing it to our *path operations*.

After that, all of the processing logic is the same.

But this way we can focus on how the **Dependency Injection** system works.

### Create a dependency, or "dependable"

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

=== "Python 3.10+"

    ```Python hl_lines="8-9"
    {!> ../../../docs_src/dependencies/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="8-11"