line.textContent = `${chars.slice(0, i)} ${percent}%`;
			if (percent>progressPercent) {
				break;
			}
        }
    }

    /**
     * Helper function for animation delays, called with `await`.
     * @param {number} time - Timeout, in ms.
     */
    _wait(time) {
        return new Promise(resolve => setTimeout(resolve, time));
    }

    /**

To do that, use the standard Python type hint <a href="https://docs.python.org/3/library/typing.html#typing.Union" class="external-link" target="_blank">`typing.Union`</a>:

!!! note

    return [{"item_id": "Foo"}]


def use_route_names_as_operation_ids(app: FastAPI) -> None:
    """
    Simplify operation IDs so that generated API clients have simpler function
    names.

    Should be called only after all routes have been added.
    """
    for route in app.routes:
        if isinstance(route, APIRoute):
            route.operation_id = route.name  # in this case, 'read_items'

## Example

For a simple example, let's consider a file structure similar to the one described in [Bigger Applications](../tutorial/bigger-applications.md){.internal-link target=_blank} and [Testing](../tutorial/testing.md){.internal-link target=_blank}:

```
.
├── app
│   ├── __init__.py

Here's a more complete example.

Use a dependency to check if the username and password are correct.

For this, use the Python standard module <a href="https://docs.python.org/3/library/secrets.html" class="external-link" target="_blank">`secrets`</a> to check the username and password.

!!! info
    You can read more about the Starlette `lifespan` handlers in <a href="https://www.starlette.io/lifespan/" class="external-link" target="_blank">Starlette's  Lifespan' docs</a>.

    If you have an older version, you would get errors when trying to use `Annotated`.

    Make sure you [Upgrade the FastAPI version](../deployment/versions.md#upgrading-the-fastapi-versions){.internal-link target=_blank} to at least 0.95.1 before using `Annotated`.

## Declare metadata

You can declare all the same parameters as for `Query`.

from typing_extensions import Annotated, Doc, ParamSpec

P = ParamSpec("P")


class BackgroundTasks(StarletteBackgroundTasks):
    """
    A collection of background tasks that will be called after a response has been
    sent to the client.

    Read more about it in the
    [FastAPI docs for Background Tasks](https://fastapi.tiangolo.com/tutorial/background-tasks/).

    ## Example

    ```python

## OpenAPI Extra

When you declare a *path operation* in your application, **FastAPI** automatically generates the relevant metadata about that *path operation* to be included in the OpenAPI schema.

!!! note "Technical details"

```

### About `__name__ == "__main__"`

The main purpose of the `__name__ == "__main__"` is to have some code that is executed when your file is called with:

<div class="termy">

```console
$ python myapp.py
```

</div>

but is not called when another file imports it, like in:

```Python
from myapp import app
```

#### More details

Let's say your file is named `myapp.py`.