@item_router.get("/")
def get_items(user_id: Optional[str] = None):
    if user_id is None:
        return [{"item_id": "i1", "user_id": "u1"}, {"item_id": "i2", "user_id": "u2"}]
    else:
        return [{"item_id": "i2", "user_id": user_id}]


@item_router.get("/{item_id}")
def get_item(item_id: str, user_id: Optional[str] = None):
    if user_id is None:
        return {"item_id": item_id}
    else:

    "path,expected_status,expected_response",
    [
        ("/items", 200, {"q": None, "skip": 0, "limit": 100}),
        ("/items?q=foo", 200, {"q": "foo", "skip": 0, "limit": 100}),
        ("/items?q=foo&skip=5", 200, {"q": "foo", "skip": 5, "limit": 100}),
        ("/items?q=foo&skip=5&limit=30", 200, {"q": "foo", "skip": 5, "limit": 30}),
        ("/users", 200, {"q": None, "skip": 0, "limit": 100}),
    ],
)

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):

    }

    public Collection<DefaultType> types() {
        return Arrays.asList(
                // Maven types
                new DefaultType(Type.POM, Language.NONE, "pom", null, false),
                new DefaultType(Type.BOM, Language.NONE, "pom", null, false),
                new DefaultType(Type.MAVEN_PLUGIN, Language.JAVA_FAMILY, "jar", null, false, JavaPathType.CLASSES),
                // Java types

    assert response.status_code == 200
    assert response.json() == {
        "item_id": 5,
        "item": {"name": "Foo", "price": 3.0, "description": None, "tax": None},
    }


@needs_py310
def test_items_6(client: TestClient):
    response = client.put(
        "/items/6",
        json={
            "item": {
                "name": "Bar",

class CustomError(Exception):
    pass


@router.websocket("/custom_error/")
async def router_ws_custom_error(websocket: WebSocket):
    raise CustomError()


def make_app(app=None, **kwargs):
    app = app or FastAPI(**kwargs)
    app.include_router(router)
    app.include_router(prefix_router, prefix="/prefix")
    app.include_router(native_prefix_route)
    return app

</div>

Das bedeutet, dass es **immer einen Wert** hat, der Wert kann jedoch manchmal `None` sein (oder `null` in JSON).

Das bedeutet, dass Clients, die Ihre API verwenden, nicht prüfen müssen, ob der Wert vorhanden ist oder nicht. Sie können davon ausgehen, dass das Feld immer vorhanden ist. In einigen Fällen hat es jedoch nur den Defaultwert `None`.

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):

        "name": "Baz",
        "description": None,
        "price": 50.2,
        "tax": 10.5,
        "tags": [],
    }


def test_put(client: TestClient):
    response = client.put(
        "/items/bar", json={"name": "Barz", "price": 3, "description": None}
    )
    assert response.json() == {
        "name": "Barz",
        "description": None,
        "price": 3,
        "tax": 10.5,

        "name": "Baz",
        "description": None,
        "price": 50.2,
        "tax": 10.5,
        "tags": [],
    }


@needs_py310
def test_put(client: TestClient):
    response = client.put(
        "/items/bar", json={"name": "Barz", "price": 3, "description": None}
    )
    assert response.json() == {
        "name": "Barz",
        "description": None,
        "price": 3,
        "tax": 10.5,