* It then takes the **response** generated by the application (by some *path operation*).
* It can do something to that **response** or run any needed code.
* Then it returns the **response**.

!!! note "Technical Details"
    If you have dependencies with `yield`, the exit code will run *after* the middleware.

    And Pydantic's `Field` returns an instance of `FieldInfo` as well.

    `Body` also returns objects of a subclass of `FieldInfo` directly. And there are others you will see later that are subclasses of the `Body` class.

    Remember that when you import `Query`, `Path`, and others from `fastapi`, those are actually functions that return special classes.

!!! tip

!!! check
    The way this dependency system is designed allows us to have different dependencies (different "dependables") that all return a `User` model.

    We are not restricted to having only one dependency that can return that type of data.

## Other models

Next, we create a custom subclass of `fastapi.routing.APIRoute` that will make use of the `GzipRequest`.

This time, it will overwrite the method `APIRoute.get_route_handler()`.

This method returns a function. And that function is what will receive a request and return a response.

Here we use it to create a `GzipRequest` from the original request.

```Python hl_lines="18-26"
{!../../../docs_src/custom_request_and_route/tutorial001.py!}
```

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

### About `{**note.dict(), "id": last_record_id}`

`note` is a Pydantic `Note` object.

`note.dict()` returns a `dict` with its data, something like:

```Python
{
    "text": "Some note",
    "completed": False,
}
```

but it doesn't have the `id` field.

```

### `HTMLResponse`

Takes some text or bytes and returns an HTML response, as you read above.

### `PlainTextResponse`

Takes some text or bytes and returns an plain text response.

```Python hl_lines="2  7  9"
{!../../../docs_src/custom_response/tutorial005.py!}
```

### `JSONResponse`

Takes some data and returns an `application/json` encoded response.

That way, using `secrets.compare_digest()` in your application code, it will be safe against this whole range of security attacks.

### Return the error

After detecting that the credentials are incorrect, return an `HTTPException` with a status code 401 (the same returned when no credentials are provided) and add the header `WWW-Authenticate` to make the browser show the login prompt again:

=== "Python 3.9+"

* It will **limit and filter** the output data to what is defined in the return type.
    * This is particularly important for **security**, we'll see more of that below.

## `response_model` Parameter

There are some cases where you need or want to return some data that is not exactly what the type declares.

    ```Python hl_lines="8  13"
    {!> ../../../docs_src/dependencies/tutorial006.py!}
    ```

### Return values

And they can return values or not, the values won't be used.

So, you can re-use a normal dependency (that returns a value) you already use somewhere else, and even though the value won't be used, the dependency will be executed:

=== "Python 3.9+"