app = FastAPI()


class Image(BaseModel):
    url: str
    name: str


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None
    tags: set[str] = set()
    image: Image | None = None


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

from pydantic import BaseModel

app = FastAPI()


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


class User(BaseModel):
    username: str
    full_name: Union[str, None] = None


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

```

////

In beiden Fällen bedeutet das, dass `item` ein `int` oder ein `str` sein kann.

#### Vielleicht `None` { #possibly-none }

Sie können deklarieren, dass ein Wert ein `str`, aber vielleicht auch `None` sein kann.

In Python 3.6 und darüber (inklusive Python 3.10) können Sie das deklarieren, indem Sie `Optional` vom `typing` Modul importieren und verwenden.

    github_repository: str
    github_token: SecretStr
    deploy_url: str | None = None
    commit_sha: str
    run_id: int
    state: Literal["pending", "success", "error"] = "pending"


class LinkData(BaseModel):
    previous_link: str
    preview_link: str
    en_link: str | None = None


def main() -> None:
    logging.basicConfig(level=logging.INFO)
    settings = Settings()

from pydantic import BaseModel

app = FastAPI()


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


class User(BaseModel):
    username: str
    full_name: Union[str, None] = None


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

from pydantic import BaseModel

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


class User(BaseModel):
    username: str
    email: str | None = None
    full_name: str | None = None
    disabled: bool | None = None


def fake_decode_token(token):
    return User(
        username=token + "fakedecoded", email="******@****.***", full_name="John Doe"
    )

```Python
q: Union[str, None] = None
```

Ou bien, en Python 3.10 et supérieur :

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

Par exemple :

{* ../../docs_src/body_multiple_params/tutorial004_an_py310.py hl[27] *}

/// info

from pydantic import BaseModel

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


class User(BaseModel):
    username: str
    email: str | None = None
    full_name: str | None = None
    disabled: bool | None = None


def fake_decode_token(token):
    return User(
        username=token + "fakedecoded", email="******@****.***", full_name="John Doe"
    )

기본값 `None`을 `Query(None)`으로 바꿔야 하므로, `Query`의 첫 번째 매개변수는 기본값을 정의하는 것과 같은 목적으로 사용됩니다.

그러므로:

```Python
q: Optional[str] = Query(None)
```

...위 코드는 아래와 동일하게 매개변수를 선택적으로 만듭니다:

```Python
q: Optional[str] = None
```

하지만 명시적으로 쿼리 매개변수를 선언합니다.

/// info | 정보

FastAPI는 다음 부분에 관심이 있습니다:

```Python
= None
```

또는:

```Python
= Query(None)

    return True


@noop_wrap
def wrapped_gen_dependency() -> Generator[bool, None, None]:
    yield True


@noop_wrap
async def async_wrapped_dependency() -> bool:
    return True


@noop_wrap
async def async_wrapped_gen_dependency() -> AsyncGenerator[bool, None]:
    yield True


@app.get("/wrapped-dependency/")