name: Privileged
description: You are @tiangolo or he asked you directly to create an issue here. If not, check the other options. 👇
body:
  - type: markdown
    attributes:
      value: |
        Thanks for your interest in FastAPI! 🚀

    ```

#### Using `Union` or `Optional`

If you are using a Python version below 3.10, here's a tip from my very **subjective** point of view:

* 🚨 Avoid using `Optional[SomeType]`
* Instead ✨ **use `Union[SomeType, None]`** ✨.

```

### f-strings

If you are not familiar with the `f"userprofile::{username}"`, it is a Python "<a href="https://docs.python.org/3/glossary.html#term-f-string" class="external-link" target="_blank">f-string</a>".

Any variable that is put inside of `{}` in an f-string will be expanded / injected in the string.

### `dict` unpacking

## Mounting a **FastAPI** application

"Mounting" means adding a completely "independent" application in a specific path, that then takes care of handling everything under that path, with the _path operations_ declared in that sub-application.

### Top-level application

First, create the main, top-level, **FastAPI** application, and its *path operations*:

In this example we are going to use **OAuth2**, with the **Password** flow, using a **Bearer** token. We do that using the `OAuth2PasswordBearer` class.

!!! info
    A "bearer" token is not the only option.

    But it's the best one for our use case.

Hiding your documentation user interfaces in production *shouldn't* be the way to protect your API.

That doesn't add any extra security to your API, the *path operations* will still be available where they are.

If there's a security flaw in your code, it will still exist.

# OpenAPI

There are several utilities to handle OpenAPI.

# Reference - Code API

Here's the reference or code API, the classes, functions, parameters, attributes, and
all the FastAPI parts you can use in your applications.

If you want to **learn FastAPI** you are much better off reading the

    ```

=== "Python 3.8+"

    ```Python hl_lines="22"
    {!> ../../../docs_src/body_multiple_params/tutorial002.py!}
    ```

In this case, **FastAPI** will notice that there are more than one body parameters in the function (two parameters that are Pydantic models).

So, it will then use the parameter names as keys (field names) in the body, and expect a body like:

```JSON
{
    "item": {
        "name": "Foo",

This code is something you can actually use in your application, save the password hashes in your database, etc.

We are going to start from where we left in the previous chapter and increment it.

## About JWT

JWT means "JSON Web Tokens".

It's a standard to codify a JSON object in a long dense string without spaces. It looks like this: