'Returns a static file storage if available in the given app.'

def __init__(self, app, *args, **kwargs):

    mod = import_module(app)
    mod_path = os.path.dirname(upath(mod.__file__))
    location = os.path.join(mod_path, self.source_dir)
    super(AppStaticStorage, self).__init__(location, *args, **kwargs)
