How to use the fair.view_old.CView.__subclasses__ function in fair

"""Configure view

    url route configure.

    :param app: Flask app object
    :param config: view's config
    :type  config: dict
    """
    from .view_old import CView

    if not view_packages:
        return
    for package_path in view_packages:
        iterate_package(import_module(package_path))

    for view in CView.__subclasses__():
        name = class_name_to_api_name(view.__name__)
        uri = '/%s/%s' % (view.__module__.split('.')[0], name)
        endpoint = '%s.%s' % (view.__module__.split('.')[0], name)
        app.add_url_rule(uri, view_func=view.as_view(endpoint, uri, app))