from typing import TypeVar

from fastapi import Depends, FastAPI
from fastapi.testclient import TestClient
from typing_extensions import Annotated

app = FastAPI()

T = TypeVar("T")

Dep = Annotated[T, Depends()]


class A:
    pass


class B:
    pass


@app.get("/a")
async def a(dep: Dep[A]):
    return {"cls": dep.__class__.__name__}


@app.get("/b")
async def b(dep: Dep[B]):

@router.websocket("/depends-err/")
async def router_ws_depends_err(websocket: WebSocket, data=Depends(ws_dependency_err)):
    pass  # pragma: no cover


async def ws_dependency_validate(x_missing: str = Header()):
    pass  # pragma: no cover


@router.websocket("/depends-validate/")
async def router_ws_depends_validate(
    websocket: WebSocket, data=Depends(ws_dependency_validate)
):

@app.get("/decorator-depends/", dependencies=[Depends(common_parameters)])
async def decorator_depends():
    return {"in": "decorator-depends"}


@router.get("/router-depends/")
async def router_depends(commons: dict = Depends(common_parameters)):
    return {"in": "router-depends", "params": commons}


@router.get("/router-decorator-depends/", dependencies=[Depends(common_parameters)])
async def router_decorator_depends():

def get_parameterless_sub_dependant(*, depends: params.Depends, path: str) -> Dependant:
    assert callable(
        depends.dependency
    ), "A parameter-less dependency must have a callable dependency"
    return get_sub_dependant(depends=depends, dependency=depends.dependency, path=path)


def get_sub_dependant(
    *,
    depends: params.Depends,
    dependency: Callable[..., Any],
    path: str,

    db_user = crud.get_user_by_email(db, email=user.email)
    if db_user:
        raise HTTPException(status_code=400, detail="Email already registered")
    return crud.create_user(db=db, user=user)


@app.get("/users/", response_model=list[schemas.User])
def read_users(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
    users = crud.get_users(db, skip=skip, limit=limit)
    return users

        return foo

    with pytest.raises(
        AssertionError,
        match=(
            "Cannot specify `Depends` in `Annotated` and default value"
            " together for 'foo'"
        ),
    ):

        @app.get("/")
        async def get2(foo: Annotated[int, Depends(dep)] = Depends(dep)):
            pass  # pragma: nocover

    with pytest.raises(
        AssertionError,
        match=(

def test_body_repr_list():
    assert repr(Body([])) == "Body([])"


def test_depends_repr():
    assert repr(Depends()) == "Depends(NoneType)"
    assert repr(Depends(get_user)) == "Depends(get_user)"
    assert repr(Depends(use_cache=False)) == "Depends(NoneType, use_cache=False)"
    assert (
        repr(Depends(get_user, use_cache=False)) == "Depends(get_user, use_cache=False)"

    ```

**FastAPI** 调用 `CommonQueryParams` 类。这将创建该类的一个 "实例"，该实例将作为参数 `commons` 被传递给你的函数。

## 类型注解 vs `Depends`

注意，我们在上面的代码中编写了两次`CommonQueryParams`：

```Python
commons: CommonQueryParams = Depends(CommonQueryParams)
```

最后的 `CommonQueryParams`:

```Python
... = Depends(CommonQueryParams)
```

...实际上是 **Fastapi** 用来知道依赖项是什么的。

FastAPI 将从依赖项中提取声明的参数，这才是 FastAPI 实际调用的。

    ```

=== "Python 3.8 non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python
    commons: CommonQueryParams = Depends()
    ```

You declare the dependency as the type of the parameter, and you use `Depends()` without any parameter, instead of having to write the full class *again* inside of `Depends(CommonQueryParams)`.

    ## Usage

    Create an instance object and use that object as the dependency in `Depends()`.

    The dependency result will be a string containing the key value.

    ## Example

    ```python
    from fastapi import Depends, FastAPI
    from fastapi.security import APIKeyQuery

    app = FastAPI()

    query_scheme = APIKeyQuery(name="api_key")