/// info

Notice how `Offer` has a list of `Item`s, which in turn have an optional list of `Image`s

///

## Bodies of pure lists

If the top level value of the JSON body you expect is a JSON `array` (a Python `list`), you can declare the type in the parameter of the function, the same as in Pydantic models:

```Python
images: List[Image]
```

or in Python 3.9 and above:

```Python
images: list[Image]

There are some extra features to handle security apart from the ones covered in the [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

/// tip

The next sections are **not necessarily "advanced"**.

And it's possible that for your use case, the solution is in one of them.

///

## Read the Tutorial first

// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

$ $Env:MY_NAME = "Wade Wilson"

// And then call the program again
$ python main.py

// Now it can read the environment variable

Hello Wade Wilson from Python
```

</div>

////

As environment variables can be set outside of the code, but can be read by the code, and don't have to be stored (committed to `git`) with the rest of the files, it's common to use them for configurations or **settings**.

There are several custom response classes you can use to create an instance and return them directly from your *path operations*.

Read more about it in the [FastAPI docs for Custom Response - HTML, Stream, File, others](https://fastapi.tiangolo.com/advanced/custom-response/).

You can import them directly from `fastapi.responses`:

```python
from fastapi.responses import (
    FileResponse,
    HTMLResponse,

These status codes have a name associated to recognize them, but the important part is the number.

In short:

* `100` and above are for "Information". You rarely use them directly.  Responses with these status codes cannot have a body.
* **`200`** and above are for "Successful" responses. These are the ones you would use the most.

In an advanced scenario where you know you need the dependency to be called at every step (possibly multiple times) in the same request instead of using the "cached" value, you can set the parameter `use_cache=False` when using `Depends`:

//// tab | Python 3.8+

For VMs, the standard flow is for the user to provision a short-lived JWT token onto the VM. After the initial
CSR, certificates are written to disk and mTLS is used for future requests. If the VM restarted, it would continue
to use the certificates written to disk, assuming the downtime is less than certificate expiration. This is why

Check the in-code annotation tips above to see more specific details.

## Learn More

You can also combine `dataclasses` with other Pydantic models, inherit from them, include them in your own models, etc.

To learn more, check the <a href="https://docs.pydantic.dev/latest/concepts/dataclasses/" class="external-link" target="_blank">Pydantic docs about dataclasses</a>.

## Version

You can also declare the `Response` parameter in dependencies, and set headers (and cookies) in them.

## Return a `Response` directly

You can also add headers when you return a `Response` directly.