app = FastAPI()
router = APIRouter()


@router.get("/a", responses={501: {"description": "Error 1"}})
async def a():
    return "a"


@router.get(
    "/b",
    responses={
        502: {"description": "Error 2"},
        "4XX": {"description": "Error with range, upper"},
    },
)
async def b():
    return "b"


@router.get(
    "/c",
    responses={

    price: float
    tax: float = 10.5
    tags: list[str] = []


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},
    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}


@app.get("/items/{item_id}", response_model=Item, response_model_exclude_unset=True)

    price: float
    tax: float = 10.5


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The Bar fighters", "price": 62, "tax": 20.2},
    "baz": {
        "name": "Baz",
        "description": "There goes my baz",
        "price": 50.2,
        "tax": 10.5,
    },
}


@app.get(
    "/items/{item_id}/name",
    response_model=Item,

    price: float
    tax: float = 10.5


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The Bar fighters", "price": 62, "tax": 20.2},
    "baz": {
        "name": "Baz",
        "description": "There goes my baz",
        "price": 50.2,
        "tax": 10.5,
    },
}


@app.get(
    "/items/{item_id}/name",
    response_model=Item,

    price: Union[float, None] = None
    tax: float = 10.5
    tags: list[str] = []


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},
    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}


@app.get("/items/{item_id}", response_model=Item)
async def read_item(item_id: str):
    return items[item_id]

     *
     * @param server the server name
     * @param sharename the name of the share to query
     */
    public MsrpcShareGetInfo(final String server, final String sharename) {
        super(server, sharename, 502, new srvsvc.ShareInfo502());
        this.ptype = 0;
        this.flags = DCERPC_FIRST_FRAG | DCERPC_LAST_FRAG;
    }

    /**
     * Returns the security descriptor of the share as an array of ACEs.
     *

     *
     * @param server the server name
     * @param sharename the name of the share to query
     */
    public MsrpcShareGetInfo(final String server, final String sharename) {
        super(server, sharename, 502, new srvsvc.ShareInfo502());
        ptype = 0;
        flags = DCERPC_FIRST_FRAG | DCERPC_LAST_FRAG;
    }

    /**
     * Returns the security descriptor of the share as an array of ACEs.
     *

    response = client.get("/items/baz")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "name": "Baz",
        "description": None,
        "price": 50.2,
        "tax": 10.5,
        "tags": [],
    }


def test_patch_all(client: TestClient):
    response = client.patch(
        "/items/foo",
        json={
            "name": "Fooz",

    response = client.get("/items/baz")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "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}
    )

{* ../../docs_src/response_model/tutorial004.py hl[24] *}

然后响应中将不会包含那些默认值，而是仅有实际设置的值。

因此，如果你向*路径操作*发送 ID 为 `foo` 的商品的请求，则响应（不包括默认值）将为：

```JSON
{
    "name": "Foo",
    "price": 50.2
}
```

/// info

FastAPI 通过 Pydantic 模型的 `.dict()` 配合 <a href="https://docs.pydantic.dev/latest/concepts/serialization/#modeldict" class="external-link" target="_blank">该方法的 `exclude_unset` 参数</a> 来实现此功能。