# Custom Response Classes - File, HTML, Redirect, Streaming, etc.

There are several custom response classes you can use to create an instance and return them directly from your *path operations*.

Read more about it in the [FastAPI docs for Custom Response - HTML, Stream, File, others](https://fastapi.tiangolo.com/advanced/custom-response/).

You can import them directly from `fastapi.responses`:

```python
from fastapi.responses import (
    FileResponse,

There are some cases where you might need to modify the generated OpenAPI schema.

In this section you will see how.

## The normal process

The normal (default) process, is as follows.

A `FastAPI` application (instance) has an `.openapi()` method that is expected to return the OpenAPI schema.

As part of the application object creation, a *path operation* for `/openapi.json` (or for whatever you set your `openapi_url`) is registered.

{
  "message": "Hello World"
}
```

Of course, you will probably find much better ways to take advantage of this than formatting JSON. 😉

## Default response class

When creating a **FastAPI** class instance or an `APIRouter` you can specify which response class to use by default.

The parameter that defines this is `default_response_class`.

    But as it's a common use case, it is provided by **FastAPI** directly, just to make it easier.

### Use the form data

!!! tip
    The instance of the dependency class `OAuth2PasswordRequestForm` won't have an attribute `scope` with the long string separated by spaces, instead, it will have a `scopes` attribute with the actual list of strings for each scope sent.

```Python hl_lines="3  8-13  31  49"
{!../../../docs_src/sql_databases_peewee/sql_app/schemas.py!}
```

Here we are checking if the attribute that is being accessed (e.g. `.items` in `some_user.items`) is an instance of `peewee.ModelSelect`.

And if that's the case, just return a `list` with it.

                This is simply inherited from Starlette.

                Read more about it in the
                [Starlette docs for Applications](https://www.starlette.io/applications/#storing-state-on-the-app-instance).
                """
            ),
        ] = State()
        self.dependency_overrides: Annotated[
            Dict[Callable[..., Any], Callable[..., Any]],
            Doc(
                """

Le mot "**serveur**" est couramment utilisé pour désigner à la fois l'ordinateur distant/cloud (la machine physique ou virtuelle) et également le programme qui s'exécute sur cette machine (par exemple, Uvicorn).

Gardez cela à l'esprit lorsque vous lisez "serveur" en général, cela pourrait faire référence à l'une de ces deux choses.

        pass

    class MyModel(BaseModel):
        dt_field: safe_datetime

    instance = MyModel(dt_field=safe_datetime.now())

    encoded_instance = jsonable_encoder(
        instance, custom_encoder={safe_datetime: lambda o: o.isoformat()}
    )
    assert encoded_instance["dt_field"] == instance.dt_field.isoformat()


def test_custom_enum_encoders():
    def custom_enum_encoder(v: Enum):

then it is a "callable".

## Classes as dependencies

You might notice that to create an instance of a Python class, you use that same syntax.

For example:

```Python
class Cat:
    def __init__(self, name: str):
        self.name = name


fluffy = Cat(name="Mr Fluffy")
```

In this case, `fluffy` is an instance of the class `Cat`.

And to create `fluffy`, you are "calling" `Cat`.

    the key value sent in the query parameter automatically and provides it as the
    dependency result. But it doesn't define how to send that API key to the client.

    ## 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