```Python hl_lines="8-11"
    {!> ../../../docs_src/dependencies/tutorial001.py!}
    ```

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

You can think of it as a *path operation function* without the "decorator" (without the `@app.get("/some-path")`).

And it can return anything you want.

In this case, this dependency expects:

    ```

Let's focus on the parameters declared:

* Even though this function is a dependency ("dependable") itself, it also declares another dependency (it "depends" on something else).
    * 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`.

To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

```Python hl_lines="16-18  21-22  28-32"

The result of calling it is something that can be encoded with the Python standard <a href="https://docs.python.org/3/library/json.html#json.dumps" class="external-link" target="_blank">`json.dumps()`</a>.

It doesn't return a large `str` containing the data in JSON format (as a string). It returns a Python standard data structure (e.g. a `dict`) with values and sub-values that are all compatible with JSON.

!!! note

By default it will listen on the IP address `127.0.0.1`, which is the IP for your machine to communicate with itself alone (`localhost`).

## `fastapi run`

When you run `fastapi run`, it will run on production mode by default.

It will have **auto-reload disabled** by default.

### Check the code

* Check and read the code, see if it makes sense, **run it locally** and see if it actually solves the problem.

* Then **comment** saying that you did that, that's how I will know you really checked it.

!!! info
    Unfortunately, I can't simply trust PRs that just have several approvals.

## Alternative (old) `Query` as the default value

Previous versions of FastAPI (before <abbr title="before 2023-03">0.95.0</abbr>) required you to use `Query` as the default value of your parameter, instead of putting it in `Annotated`, there's a high chance that you will see code using it around, so I'll explain it to you.

!!! tip

By using all the previous alternatives I had the chance to learn from all of them, take ideas, and combine them in the best way I could find for myself and the teams of developers I have worked with.

For example, it was clear that ideally it should be based on standard Python type hints.

Also, the best approach was to use already existing standards.

    'email': '******@****.***',
    'full_name': None,
}
```

#### Unwrapping a `dict`

If we take a `dict` like `user_dict` and pass it to a function (or class) with `**user_dict`, Python will "unwrap" it. It will pass the keys and values of the `user_dict` directly as key-value arguments.

So, continuing with the `user_dict` from above, writing:

```Python
UserInDB(**user_dict)
```

would result in something equivalent to:

## Deprecate a *path operation*

If you need to mark a *path operation* as <abbr title="obsolete, recommended not to use it">deprecated</abbr>, but without removing it, pass the parameter `deprecated`:

```Python hl_lines="16"
{!../../../docs_src/path_operation_configuration/tutorial006.py!}
```

It will be clearly marked as deprecated in the interactive docs:

<img src="/img/tutorial/path-operation-configuration/image04.png">