## Server-Sent Events (SSE) { #server-sent-events-sse }

 * character encoding. UTF-8 is defined in section D92 of <a
 * href="http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf">The Unicode Standard Core
 * Specification, Chapter 3</a>.
 *
 * <p>The variant of UTF-8 implemented by this class is the restricted definition of UTF-8
 * introduced in Unicode 3.1. One implication of this is that it rejects <a

 * character encoding. UTF-8 is defined in section D92 of <a
 * href="http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf">The Unicode Standard Core
 * Specification, Chapter 3</a>.
 *
 * <p>The variant of UTF-8 implemented by this class is the restricted definition of UTF-8
 * introduced in Unicode 3.1. One implication of this is that it rejects <a

That defines the metadata about the main response of a *path operation*.

You can also declare additional responses with their models, status codes, etc.

There's a whole chapter here in the documentation about it, you can read it at [Additional Responses in OpenAPI](additional-responses.md).

## OpenAPI Extra { #openapi-extra }

To see all the options you have, checkout [Pydantic's Type Overview](https://docs.pydantic.dev/latest/concepts/types/). You will see some examples in the next chapter.

For example, as in the `Image` model we have a `url` field, we can declare it to be an instance of Pydantic's `HttpUrl` instead of a `str`:

{* ../../docs_src/body_nested_models/tutorial005_py310.py hl[2,8] *}

  `Take off your hat,' the King said to the Hatter.

  `It isn't mine,' said the Hatter.

  `Stolen!' the King exclaimed, turning to the jury, who
instantly made a memorandum of the fact.

  `I keep them to sell,' the Hatter added as an explanation;
`I've none of my own.  I'm a hatter.'

  Here the Queen put on her spectacles, and began staring at the
Hatter, who turned pale and fidgeted.

And that function takes parameters in the same way that *path operation functions* do.

/// tip

You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

///

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.

  `Take off your hat,' the King said to the Hatter.

  `It isn't mine,' said the Hatter.

  `Stolen!' the King exclaimed, turning to the jury, who
instantly made a memorandum of the fact.

  `I keep them to sell,' the Hatter added as an explanation;
`I've none of my own.  I'm a hatter.'

  Here the Queen put on her spectacles, and began staring at the
Hatter, who turned pale and fidgeted.

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 { #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:

```

But even if you never use **FastAPI**, you would benefit from learning a bit about them.

/// note

If you are a Python expert, and you already know everything about type hints, skip to the next chapter.

///

## Motivation { #motivation }

Let's start with a simple example:

{* ../../docs_src/python_types/tutorial001_py310.py *}

Calling this program outputs:

```
John Doe
```