!!! check "Inspirierte **FastAPI**"
    Zusätzliche Validierungen für Datentypen zu definieren, mithilfe des „Default“-Werts von Modellattributen. Dies verbessert die Editorunterstützung und war zuvor in Pydantic nicht verfügbar.

    # Core Vocabulary
    schema_: Optional[str] = Field(default=None, alias="$schema")
    vocabulary: Optional[str] = Field(default=None, alias="$vocabulary")
    id: Optional[str] = Field(default=None, alias="$id")
    anchor: Optional[str] = Field(default=None, alias="$anchor")
    dynamicAnchor: Optional[str] = Field(default=None, alias="$dynamicAnchor")
    ref: Optional[str] = Field(default=None, alias="$ref")

            ),
        ] = None,
        default_response_class: Annotated[
            Type[Response],
            Doc(
                """
                The default response class to be used.

                Read more in the
                [FastAPI docs for Custom Response - HTML, Stream, File, others](https://fastapi.tiangolo.com/advanced/custom-response/#default-response-class).

                **Example**

## Default response class

When creating a **FastAPI** class instance or an `APIRouter` you can specify which response class to use by default.

The parameter that defines this is `default_response_class`.

In the example below, **FastAPI** will use `ORJSONResponse` by default, in all *path operations*, instead of `JSONResponse`.

```Python hl_lines="2  4"

from fastapi.encoders import jsonable_encoder
from starlette.responses import HTMLResponse
from typing_extensions import Annotated, Doc

swagger_ui_default_parameters: Annotated[
    Dict[str, Any],
    Doc(
        """
        Default configurations for Swagger UI.

        You can use it as a template to add any other configurations needed.
        """
    ),
] = {
    "dom_id": "#swagger-ui",

## Die Default-Exceptionhandler überschreiben

**FastAPI** hat einige Default-Exceptionhandler.

Diese Handler kümmern sich darum, Default-JSON-Responses zurückzugeben, wenn Sie eine `HTTPException` `raise`n, und wenn der Request ungültige Daten enthält.

Then open 10 tabs at <a href="http://127.0.0.1:8000/docs#/default/read_slow_users_slowusers__get" class="external-link" target="_blank">http://127.0.0.1:8000/docs#/default/read_slow_users_slowusers__get</a> at the same time.

def test_post_large_file(tmp_path):
    default_pydantic_max_size = 2**16
    path = tmp_path / "test.txt"
    path.write_bytes(b"x" * (default_pydantic_max_size + 1))

    client = TestClient(app)
    with path.open("rb") as file:
        response = client.post("/files/", files={"file": file})
    assert response.status_code == 200, response.text
    assert response.json() == {"file_size": default_pydantic_max_size + 1}

from typing import Union

from fastapi import FastAPI, Header

app = FastAPI()


@app.get("/items/")
async def read_items(
    strange_header: Union[str, None] = Header(default=None, convert_underscores=False),
):

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: str | None = Query(default=None, title="Query string", min_length=3),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})