Routes are declared in a single place, using functions declared in other places (instead of using decorators that can be placed right on top of the function that handles the endpoint). This is closer to how Django does it than to how Flask (and Starlette) does it. It separates in the code things that are relatively tightly coupled.

### Is concurrency better than parallelism? { #is-concurrency-better-than-parallelism }

Nope! That's not the moral of the story.

Concurrency is different than parallelism. And it is better on **specific** scenarios that involve a lot of waiting. Because of that, it generally is a lot better than parallelism for web application development. But not for everything.

So, to balance that out, imagine the following short story:

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.

## A "callable" instance { #a-callable-instance }

In Python there's a way to make an instance of a class a "callable".

Not the class itself (which is already a callable), but an instance of that class.

    SQLModel will know that something declared as `str` will be a SQL column of type `TEXT` (or `VARCHAR`, depending on the database).

### Create an Engine { #create-an-engine }

You could create an API with a *path operation* that could trigger a request to an *external API* created by someone else (probably the same developer that would be *using* your API).

The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

`secrets.compare_digest()` needs to take `bytes` or a `str` that only contains ASCII characters (the ones in English), this means it wouldn't work with characters like `á`, as in `Sebastián`.

To handle that, we first convert the `username` and `password` to `bytes` encoding them with UTF-8.

Then we can use `secrets.compare_digest()` to ensure that `credentials.username` is `"stanleyjobson"`, and that `credentials.password` is `"swordfish"`.

We also verify that we have a user with that username, and if not, we raise that same exception we created before.

{* ../../docs_src/security/tutorial005_an_py310.py hl[47,117:129] *}

## Verify the `scopes` { #verify-the-scopes }

new properties on a task, extension or domain object that use plain getters and setters.  It is also not acceptable to add setters that take a Provider.

Note that when adding a lazy property to an existing class, you need to check if instances of the class are instantiated via ObjectFactory. Most classes are instantiated this way, but it's possible that a class without any lazy properties was never updated to use it. A tell-tale sign that an object is not instantiated via the ObjectFactory...

  HttpUrl baseUrl = server.url("/v1/chat/");

  // Exercise your application code, which should make those HTTP requests.
  // Responses are returned in the same order that they are enqueued.
  Chat chat = new Chat(baseUrl);

  chat.loadMore();
  assertEquals("hello, world!", chat.messages());

  chat.loadMore();
  chat.loadMore();
  assertEquals(""
      + "hello, world!\n"

The `@app.get("/")` tells **FastAPI** that the function right below is in charge of handling requests that go to:

* the path `/`
* using a <abbr title="an HTTP GET method"><code>get</code> operation</abbr>

/// info | `@decorator` Info

That `@something` syntax in Python is called a "decorator".

You put it on top of a function. Like a pretty decorative hat (I guess that's where the term came from).