Returns appropriate swagger handler and swagger spec schema.

    Swagger Handler contains callables that isolate implementation differences
    in the tween to handle both Swagger 1.2 and Swagger 2.0.

    Exception is made when `settings.prefer_20_routes` are non-empty and
    ['1.2', '2.0'] both are present in available swagger versions. In this
    special scenario, '2.0' spec is chosen only for requests which are listed
    in the `prefer_20_routes`. This helps in incremental migration of
    routes from v1.2 to v2.0 by making moving to v2.0 opt-in.

    :rtype: (:class:`SwaggerHandler`,
             :class:`pyramid_swagger.model.SwaggerSchema` OR
                :class:`bravado_core.spec.Spec`)

def get_swagger_objects(settings, route_info, registry):
    """Returns appropriate swagger handler and swagger spec schema.

    Swagger Handler contains callables that isolate implementation differences
    in the tween to handle both Swagger 1.2 and Swagger 2.0.

    Exception is made when `settings.prefer_20_routes` are non-empty and
    ['1.2', '2.0'] both are present in available swagger versions. In this
    special scenario, '2.0' spec is chosen only for requests which are listed
    in the `prefer_20_routes`. This helps in incremental migration of
    routes from v1.2 to v2.0 by making moving to v2.0 opt-in.

    :rtype: (:class:`SwaggerHandler`,
             :class:`pyramid_swagger.model.SwaggerSchema` OR
                :class:`bravado_core.spec.Spec`)
    """
    enabled_swagger_versions = get_swagger_versions(registry.settings)
    schema12 = registry.settings['pyramid_swagger.schema12']
    schema20 = registry.settings['pyramid_swagger.schema20']

    fallback_to_swagger12_route = (
        SWAGGER_20 in enabled_swagger_versions and
        SWAGGER_12 in enabled_swagger_versions and
        settings.prefer_20_routes and
        route_info.get('route') and
        route_info['route'].name not in settings.prefer_20_routes
    )
    if fallback_to_swagger12_route:
        return settings.swagger12_handler, schema12

    if SWAGGER_20 in enabled_swagger_versions:
        return settings.swagger20_handler, schema20

    if SWAGGER_12 in enabled_swagger_versions:
        return settings.swagger12_handler, schema12