```Python hl_lines="8"
{!../../../docs_src/events/tutorial001.py!}
```

In this case, the `startup` event handler function will initialize the items "database" (just a `dict`) with some values.

You can add more than one event handler function.

And your application won't start receiving requests until all the `startup` event handlers have completed.

### `shutdown` event

# Separate OpenAPI Schemas for Input and Output or Not

When using **Pydantic v2**, the generated OpenAPI is a bit more exact and **correct** than before. 😎

In fact, in some cases, it will even have **two JSON Schemas** in OpenAPI for the same Pydantic model, for input and output, depending on if they have **default values**.

Let's see how that works and how to change it if you need to do that.

## Pydantic Models for Input and Output

Aqui é onde se torna importante a possibilidade de declarar <abbr title="greater than"><code>gt</code></abbr> e não apenas <abbr title="greater than or equal"><code>ge</code></abbr>. Com isso você pode especificar, por exemplo, que um valor deve ser maior que `0`, ainda que seja menor que `1`.

Assim, `0.5` seria um valor válido. Mas `0.0` ou `0` não seria.

E o mesmo para <abbr title="less than"><code>lt</code></abbr>.

```Python hl_lines="11"

    assert response.status_code == 422
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "greater_than",
                    "loc": ["body", "item", "price"],
                    "msg": "Input should be greater than 0",
                    "input": -3.0,
                    "ctx": {"gt": 0.0},
                }
            ]
        }
    ) | IsDict(

    assert response.status_code == 422
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "greater_than",
                    "loc": ["body", "item", "price"],
                    "msg": "Input should be greater than 0",
                    "input": -3.0,
                    "ctx": {"gt": 0.0},
                }
            ]
        }
    ) | IsDict(

You probably read before that you can set a default [Response Status Code](../tutorial/response-status-code.md){.internal-link target=_blank}.

But in some cases you need to return a different status code than the default.

## Use case

For example, imagine that you want to return an HTTP status code of "OK" `200` by default.

But if the data didn't exist, you want to create it, and return an HTTP status code of "CREATED" `201`.

## Origin

An origin is the combination of protocol (`http`, `https`), domain (`myapp.com`, `localhost`, `localhost.tiangolo.com`), and port (`80`, `443`, `8080`).

So, all these are different origins:

This means that you can send only the data that you want to update, leaving the rest intact.

!!! note
    `PATCH` is less commonly used and known than `PUT`.

    And many teams use only `PUT`, even for partial updates.

    You are **free** to use them however you want, **FastAPI** doesn't impose any restrictions.

## Uvicorn with Workers

Uvicorn also has an option to start and run several **worker processes**.

Nevertheless, as of now, Uvicorn's capabilities for handling worker processes are more limited than Gunicorn's. So, if you want to have a process manager at this level (at the Python level), then it might be better to try with Gunicorn as the process manager.

In any case, you would run it like this:

<div class="termy">