//// tab | Python 3.8+

```Python hl_lines="1"
async def needy_dependency(fresh_value: Annotated[str, Depends(get_value, use_cache=False)]):
    return {"fresh_value": fresh_value}
```

////

//// tab | Python 3.8+ non-Annotated

/// tip

Prefer to use the `Annotated` version if possible.

///

```Python hl_lines="1"

    再一次，可以把 `dataclasses` 与标准类型注解一起使用；

8. 注意，*路径操作函数*使用的是普通函数，不是异步函数；

    与往常一样，在 FastAPI 中，可以按需组合普通函数与异步函数；

    如果不清楚何时使用异步函数或普通函数，请参阅**急不可待？**一节中对 <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank" class="internal-link">`async` 与 `await`</a> 的说明；

9. *路径操作函数*返回的不是数据类（虽然它可以返回数据类），而是返回内含数据的字典列表；

    FastAPI 使用（包含数据类的） `response_model` 参数转换响应。

把 `dataclasses` 与其它类型注解组合在一起，可以组成不同形式的复杂数据结构。

更多内容详见上述代码内的注释。

from pydantic import BaseModel


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


app = FastAPI()


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item, q: str | None = None):
    result = {"item_id": item_id, **item.dict()}
    if q:
        result.update({"q": q})

from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


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

app = FastAPI()


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


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

    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None
    tags: Set[str] = set()


@app.post("/items/", response_model=Item, status_code=status.HTTP_201_CREATED)
async def create_item(item: Item):

class FilterParams(BaseModel):
    limit: int = Field(100, gt=0, le=100)
    offset: int = Field(0, ge=0)
    order_by: Literal["created_at", "updated_at"] = "created_at"
    tags: list[str] = []


@app.get("/items/")
async def read_items(filter_query: FilterParams = Query()):

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


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

from typing_extensions import Annotated

app = FastAPI()


class FormData(BaseModel):
    username: str
    password: str

    class Config:
        extra = "forbid"


@app.post("/login/")
async def login(data: Annotated[FormData, Form()]):

from fastapi import FastAPI, Path

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(*, item_id: int = Path(title="The ID of the item to get"), q: str):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})