from typing import Union

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Item = Body(
        openapi_examples={
            "normal": {

```

由于我们必须用 `Query(default=None)` 替换默认值 `None`，`Query` 的第一个参数同样也是用于定义默认值。

所以：

```Python
q: Union[str, None] = Query(default=None)
```

...使得参数可选，等同于：

```Python
q: str = None
```

但是 `Query` 显式地将其声明为查询参数。

然后，我们可以将更多的参数传递给 `Query`。在本例中，适用于字符串的 `max_length` 参数：

```Python
q: Union[str, None] = Query(default=None, max_length=50)
```

      "gridPos": {
        "h": 4,
        "w": 8,
        "x": 0,
        "y": 4
      },
      "id": 12,
      "links": [],
      "maxDataPoints": 100,
      "options": {
        "colorMode": "none",
        "graphMode": "area",
        "justifyMode": "auto",
        "orientation": "horizontal",
        "reduceOptions": {
          "calcs": [
            "lastNotNull"
          ],

async def override_dependency(q: Union[str, None] = None):
    return {"q": q, "skip": 5, "limit": 10}


app.dependency_overrides[common_parameters] = override_dependency


def test_override_in_items():
    response = client.get("/items/")
    assert response.status_code == 200
    assert response.json() == {
        "message": "Hello Items!",
        "params": {"q": None, "skip": 5, "limit": 10},
    }

    client = TestClient(app)
    return client


def test_create_item(client: TestClient) -> None:
    response = client.post("/items/", json={"name": "Foo"})
    assert response.status_code == 200, response.text
    assert response.json() == {"name": "Foo", "description": None}


def test_read_items(client: TestClient) -> None:
    response = client.get("/items/")
    assert response.status_code == 200, response.text

    return client


@needs_py39
def test_create_item(client: TestClient) -> None:
    response = client.post("/items/", json={"name": "Foo"})
    assert response.status_code == 200, response.text
    assert response.json() == {"name": "Foo", "description": None}


@needs_py39
def test_read_items(client: TestClient) -> None:
    response = client.get("/items/")
    assert response.status_code == 200, response.text

from typing import Annotated, Union

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Annotated[
        Item,
        Body(
            openapi_examples={

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list[str] | None, Query()] = None):
    query_items = {"q": q}

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),
):

COMMIT
* raw
-N ISTIO_OUTPUT
-N ISTIO_PRERT
-A PREROUTING -j ISTIO_PRERT
-A OUTPUT -j ISTIO_OUTPUT
-A ISTIO_OUTPUT -p udp -m mark --mark 0x539/0xfff -m udp --dport 53 -j CT --zone 1
-A ISTIO_PRERT -p udp -m mark ! --mark 0x539/0xfff -m udp --sport 53 -j CT --zone 1
COMMIT
* mangle
-N ISTIO_PRERT
-N ISTIO_OUTPUT
-A PREROUTING -j ISTIO_PRERT
-A OUTPUT -j ISTIO_OUTPUT