假设要创建校验查询参数 `q` 是否包含固定内容的依赖项。

但此处要把待检验的固定内容定义为参数。

## **可调用**实例

Python 可以把类实例变为**可调用项**。

这里说的不是类本身（类本就是可调用项），而是类实例。

为此，需要声明 `__call__` 方法：

```Python hl_lines="10"
{!../../docs_src/dependencies/tutorial011.py!}
```

本例中，**FastAPI**  使用 `__call__` 检查附加参数及子依赖项，稍后，还要调用它向*路径操作函数*传递值。

## 参数化实例

接下来，使用 `__init__` 声明用于**参数化**依赖项的实例参数：

```Python hl_lines="7"

            openIdConnectUrl=openIdConnectUrl, description=description
        )
        self.scheme_name = scheme_name or self.__class__.__name__
        self.auto_error = auto_error

    async def __call__(self, request: Request) -> Optional[str]:
        authorization = request.headers.get("Authorization")
        if not authorization:
            if self.auto_error:
                raise HTTPException(

            flows=cast(OAuthFlowsModel, flows), description=description
        )
        self.scheme_name = scheme_name or self.__class__.__name__
        self.auto_error = auto_error

    async def __call__(self, request: Request) -> Optional[str]:
        authorization = request.headers.get("Authorization")
        if not authorization:
            if self.auto_error:
                raise HTTPException(

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")

In Python gibt es eine Möglichkeit, eine Instanz einer Klasse „aufrufbar“ („callable“) zu machen.

Nicht die Klasse selbst (die bereits aufrufbar ist), sondern eine Instanz dieser Klasse.

Dazu deklarieren wir eine Methode `__call__`:

//// tab | Python 3.9+

```Python hl_lines="12"
{!> ../../docs_src/dependencies/tutorial011_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="11"

            name=name,
            description=description,
        )
        self.scheme_name = scheme_name or self.__class__.__name__
        self.auto_error = auto_error

    async def __call__(self, request: Request) -> Optional[str]:
        api_key = request.query_params.get(self.model.name)
        if not api_key:
            if self.auto_error:
                raise HTTPException(

                        "code": 999,
                        "message": "File limit exceeded",
                    },
                )
            return message

        return inner

    async def __call__(self, scope, receive, send):
        if scope["type"] != "http" or self.max_content_size is None:
            await self.app(scope, receive, send)
            return

        wrapper = self.receive_wrapper(receive)

    if inspect.isclass(call):
        return False
    dunder_call = getattr(call, "__call__", None)  # noqa: B004
    return inspect.iscoroutinefunction(dunder_call)


def is_async_gen_callable(call: Callable[..., Any]) -> bool:
    if inspect.isasyncgenfunction(call):
        return True
    dunder_call = getattr(call, "__call__", None)  # noqa: B004
    return inspect.isasyncgenfunction(dunder_call)

 # define weak_extern(symbol) _weak_extern (weak symbol)
@@ -528,7 +536,8 @@ for linking")
 #  define __hidden_ver1(local, internal, name) \
   extern __typeof (name) __EI_##name __asm__(__hidden_asmname (#internal)); \
   extern __typeof (name) __EI_##name \
-	__attribute__((alias (__hidden_asmname (#local))))
+    __attribute__((alias (__hidden_asmname (#local))))	\
+    __attribute_copy__ (name)

        "tagsQuery": "",
        "type": "custom",
        "useTags": false
      },
      {
        "current": {
          "selected": false,
          "text": "All",
          "value": "$__all"
        },
        "datasource": {
          "type": "prometheus",
          "uid": "${datasource}"
        },
        "definition": "",
        "hide": 0,
        "includeAll": true,