from pydantic import BaseModel


class Item(BaseModel):
    id: str
    value: str


class Message(BaseModel):
    message: str


app = FastAPI()


@app.get("/items/{item_id}", response_model=Item, responses={404: {"model": Message}})
async def read_item(item_id: str):
    if item_id == "foo":
        return {"id": "foo", "value": "there goes my hero"}

  // HEAD requests never yield a body regardless of the response headers.
  if (request.method == "HEAD") {
    return false
  }

  val responseCode = code
  if ((responseCode < HTTP_CONTINUE || responseCode >= 200) &&
    responseCode != HTTP_NO_CONTENT &&
    responseCode != HTTP_NOT_MODIFIED
  ) {
    return true
  }

  // If the Content-Length or Transfer-Encoding headers disagree with the response code, the

    raise exc


@app.get("/users/{user_id}")
def get_user(user_id: int):
    return {"user_id": user_id}  # pragma: no cover


@app.get("/items/", response_model=Item)
def get_item():
    return {"name": "Widget"}


@sub_app.get("/items/", response_model=Item)
def get_sub_item():
    return {"name": "Widget"}  # pragma: no cover


@app.websocket("/ws/{item_id}")

            return dt_field.replace(microsecond=0, tzinfo=timezone.utc).isoformat()

    app = FastAPI()
    model = ModelWithDatetimeField(dt_field=datetime(2019, 1, 1, 8))

    @app.get("/model", response_model=ModelWithDatetimeField)
    def get_model():
        return model

    client = TestClient(app)
    with client:
        response = client.get("/model")

                    `response_model` would be used to serialize that object into the
                    corresponding JSON.
                * Filtering: the JSON sent to the client will only contain the data
                    (fields) defined in the `response_model`. If you returned an object
                    that contains an attribute `password` but the `response_model` does

然后你可以在这个*临时*响应对象中设置头部。
{* ../../docs_src/response_headers/tutorial002.py hl[1,7:8] *}

然后你可以像平常一样返回任何你需要的对象（例如一个`dict`或者一个数据库模型）。如果你声明了一个`response_model`，它仍然会被用来过滤和转换你返回的对象。

**FastAPI**将使用这个临时响应来提取头部（也包括cookies和状态码），并将它们放入包含你返回的值的最终响应中，该响应由任何`response_model`过滤。

你也可以在依赖项中声明`Response`参数，并在其中设置头部（和cookies）。

## 直接返回 `Response`

你也可以在直接返回`Response`时添加头部。

from fastapi import FastAPI

app = FastAPI()


@app.get("/keyword-weights/", response_model=dict[str, float])
async def read_keyword_weights():

    buf.readShort() // query id

    val flags = buf.readShort().toInt() and 0xffff
    require(flags shr 15 != 0) { "not a response" }

    val responseCode = flags and 0xf

    if (responseCode == NXDOMAIN) {
      throw UnknownHostException("$hostname: NXDOMAIN")
    } else if (responseCode == SERVFAIL) {
      throw UnknownHostException("$hostname: SERVFAIL")
    }

    val questionCount = buf.readShort().toInt() and 0xffff

    class ModelWithRef(BaseModel):
        ref: str = Field(validation_alias="$ref", serialization_alias="$ref")
        model_config = ConfigDict(validate_by_alias=True, serialize_by_alias=True)

    @app.get("/", response_model=ModelWithRef)
    async def read_root() -> Any:
        return {"$ref": "some-ref"}

    client = TestClient(app)
    return client


def test_get(client: TestClient):
    response = client.get("/")

app = FastAPI()


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