public void write(char[] cbuf, int off, int len) throws IOException {
        super.write(cbuf, off, len);
        flush();
      }

      @Override
      public void write(String str, int off, int len) throws IOException {
        super.write(str, off, len);
        flush();
      }
    };
  }

from dataclasses import dataclass, field
from typing import List, Union

from fastapi import FastAPI


@dataclass
class Item:
    name: str
    price: float
    tags: List[str] = field(default_factory=list)
    description: Union[str, None] = None
    tax: Union[float, None] = None


app = FastAPI()


@app.get("/items/next", response_model=Item)
async def read_next_item():
    return {

from fastapi import FastAPI
from pydantic import BaseModel

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, tags=["items"])
async def create_item(item: Item):
    return item


@app.get("/items/", tags=["items"])
async def read_items():

* 변수 `prices`는 `dict`이다:
    * `dict`의 키(key)는 `str`타입이다. (각 아이템의 이름(name))
    * `dict`의 값(value)는 `float`타입이다. (각 아이템의 가격(price))

#### `Optional`

`str`과 같이 타입을 선언할 때 `Optional`을 쓸 수도 있는데, "선택적(Optional)"이기때문에 `None`도 될 수 있습니다:

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

`Optional[str]`을 `str` 대신 쓰게 되면, 특정 값이 실제로는 `None`이 될 수도 있는데 항상 `str`이라고 가정하는 상황에서 에디터가 에러를 찾게 도와줄 수 있습니다.

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.post(
    "/items/",
    response_model=Item,
    summary="Create an item",

from pydantic import BaseModel

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}")

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 = Path(title="The ID of the item to get", ge=0, le=1000),
    q: str | None = None,
    item: Item | None = None,
):
    results = {"item_id": item_id}
    if q:

     * drop escaped separators (i.e '\,').
     *
     * @param str  the <code>String</code> to unescape, may be null
     * @return the processed string
     * @throws IllegalArgumentException if the Writer is <code>null</code>
     */
    protected static String unescapeJava(String str) {
        if (str == null) {
            return null;
        }
        int sz = str.length();
        StringBuilder out = new StringBuilder(sz);

class RecursiveItem(BaseModel):
    sub_items: List["RecursiveItem"] = []
    name: str


RecursiveItem.update_forward_refs()


class RecursiveSubitemInSubmodel(BaseModel):
    sub_items2: List["RecursiveItemViaSubmodel"] = []
    name: str


class RecursiveItemViaSubmodel(BaseModel):
    sub_items1: List[RecursiveSubitemInSubmodel] = []
    name: str


RecursiveSubitemInSubmodel.update_forward_refs()

class LabelSettings(BaseModel):
    await_label: str | None = None
    number: int


default_config = {"approved-2": LabelSettings(await_label="awaiting-review", number=2)}


class Settings(BaseSettings):
    github_repository: str
    token: SecretStr
    debug: bool | None = False
    config: dict[str, LabelSettings] | Literal[""] = default_config


settings = Settings()