In many cases they will only copy a fragment of the code, but that's not enough to **reproduce the problem**.

    * It depends on the `query_extractor`, and assigns the value returned by it to the parameter `q`.
* It also declares an optional `last_query` cookie, as a `str`.
    * If the user didn't provide any query `q`, we use the last query used, which we saved to a cookie before.

## Use the dependency

Then we can use the dependency with:

=== "Python 3.10+"

    ```Python hl_lines="23"

!!! check
    OpenAPI specifies that each *path operation* requires a response description.

    So, if you don't provide one, **FastAPI** will automatically generate one of "Successful response".

<img src="/img/tutorial/path-operation-configuration/image03.png">

## Deprecate a *path operation*

* <a href="https://github.com/swagger-api/swagger-ui" class="external-link" target="_blank"><strong>Swagger UI</strong></a>, propose une documentation interactive. Vous permet de directement tester l'API depuis votre navigateur.

![Swagger UI interaction](https://fastapi.tiangolo.com/img/index/index-03-swagger-02.png)

And then, that system (in this case **FastAPI**) will take care of doing whatever is needed to provide your code with those needed dependencies ("inject" the dependencies).

This is very useful when you need to:

* Have shared logic (the same code logic again and again).
* Share database connections.

    ```Python
    = Query(default=None)
    ```

    as it will use that `None` as the default value, and that way make the parameter **not required**.

    The `Union[str, None]` part allows your editor to provide better support, but it is not what tells FastAPI that this parameter is not required.

Then, we can pass more parameters to `Query`. In this case, the `max_length` parameter that applies to strings:

```Python

And it shows their true commitment to FastAPI and its **community** (you), as they not only want to provide you a **good learning experience** but also want to make sure you have a **good and healthy framework**, FastAPI. 🙇

You might want to try their courses:

    hashed_password: str


def get_user(db, username: str):
    if username in db:
        user_dict = db[username]
        return UserInDB(**user_dict)


def fake_decode_token(token):
    # This doesn't provide any security at all
    # Check the next version
    user = get_user(fake_users_db, token)
    return user


async def get_current_user(token: Annotated[str, Depends(oauth2_scheme)]):

    hashed_password: str


def get_user(db, username: str):
    if username in db:
        user_dict = db[username]
        return UserInDB(**user_dict)


def fake_decode_token(token):
    # This doesn't provide any security at all
    # Check the next version
    user = get_user(fake_users_db, token)
    return user


async def get_current_user(token: Annotated[str, Depends(oauth2_scheme)]):

But Python 3.7 and above provide a more advanced alternative to `threading.local`, that can also be used in the places where `threading.local` would be used, but is compatible with the new async features.