def __str__(self):
        return self.uuid

    @property  # type: ignore
    def __class__(self):
        return uuid.UUID

    @property
    def __dict__(self):
        """Spoof a missing __dict__ by raising TypeError, this is how
        asyncpg.pgroto.pgproto.UUID behaves"""
        raise TypeError("vars() argument must have __dict__ attribute")


@needs_pydanticv2
def test_pydanticv2():

    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
        app = FastAPI()

        @app.post("/")
        async def root(f: bytes = File()):
            return f  # pragma: nocover


def test_incorrect_multipart_installed_multi_form(monkeypatch):
    monkeypatch.delattr("multipart.multipart.parse_options_header", raising=False)

The benefit of raising an exception over `return`ing a value will be more evident in the section about Dependencies and Security.

In this example, when the client requests an item by an ID that doesn't exist, raise an exception with a status code of `404`:

    response = client.get("/query/int?query=42.5")
    assert response.status_code == 422
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "int_parsing",
                    "loc": ["query", "query"],
                    "msg": "Input should be a valid integer, unable to parse string as an integer",
                    "input": "42.5",
                }
            ]

## Data validation

But if you go to the browser at <a href="http://127.0.0.1:8000/items/foo" class="external-link" target="_blank">http://127.0.0.1:8000/items/foo</a>, you will see a nice HTTP error of:

```JSON
{
  "detail": [
    {
      "type": "int_parsing",
      "loc": [
        "path",
        "item_id"
      ],

                },
                {
                    "type": "int_parsing",
                    "loc": ["query", "skip"],
                    "msg": "Input should be a valid integer, unable to parse string as an integer",
                    "input": "a",
                },
                {
                    "type": "int_parsing",
                    "loc": ["query", "limit"],

    Ceci vous permettra d'obtenir des fonctionnalités de l'éditeur dans votre fonction, telles
    que des vérifications d'erreur, de l'auto-complétion, etc.

## <abbr title="aussi appelé sérialisation, ou parfois parsing ou marshalling en anglais">Conversion</abbr> de données

```Python hl_lines="3"
{!../../../docs_src/behind_a_proxy/tutorial002.py!}
```

Passing the `root_path` to `FastAPI` would be the equivalent of passing the `--root-path` command line option to Uvicorn or Hypercorn.

### About `root_path`

Keep in mind that the server (Uvicorn) won't use that `root_path` for anything else than passing it to the app.

    assert response.status_code == 422, response.text
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "int_parsing",
                    "loc": ["body", "size"],
                    "msg": "Input should be a valid integer, unable to parse string as an integer",
                    "input": "XL",
                }
            ],

If everything is working, or after you make the necessary changes, and all your tests are passing, then you can pin your `fastapi` to that new recent version.

## About Starlette

You shouldn't pin the version of `starlette`.

Different versions of **FastAPI** will use a specific newer version of Starlette.