```

////

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.

</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

from fastapi.testclient import TestClient

app = FastAPI()


@app.get("/query")
def read_query(q: Union[str, None]):
    return q


@app.get("/explicit-query")
def read_explicit_query(q: Union[str, None] = Query()):
    return q


@app.post("/body-embed")
def send_body_embed(b: Union[str, None] = Body(embed=True)):
    return b


client = TestClient(app)


def test_required_nonable_query_invalid():

デフォルト値`None`を`Query(default=None)`に置き換える必要があるので、`Query`の最初の引数はデフォルト値を定義するのと同じです。

なので:

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

...を以下と同じようにパラメータをオプションにします:

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

しかし、これはクエリパラメータとして明示的に宣言しています。

/// info | 情報

FastAPIは以下の部分を気にすることを覚えておいてください:

```Python
= None
```

もしくは:

```Python

```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 fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")
async def read_items(commons: CommonQueryParams = Depends()):
    response = {}

class AsyncExitStackMiddleware:
    def __init__(
        self, app: ASGIApp, context_name: str = "fastapi_middleware_astack"
    ) -> None:
        self.app = app
        self.context_name = context_name

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        async with AsyncExitStack() as stack:
            scope[self.context_name] = stack

    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/")

    print("LLM translatable languages:", translatable_langs)
    return translatable_langs


@app.command()
def llm_translatable_json(
    language: Annotated[str | None, typer.Option(envvar="LANGUAGE")] = None,
) -> None:
    translatable_langs = get_llm_translatable()
    if language:
        if language in translatable_langs:
            print(json.dumps([language]))
            return
        else:

from fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")
async def read_items(commons: Annotated[CommonQueryParams, Depends()]):