code: def create(cls, class_name, **attributes):
          
          object_class = cls.extend(class_name)
          return object_class(**attributes)
docs: 根据参数创建一个 leancloud.Object 的子类的实例化对象
  
          :param class_name: 子类名称
          :type class_name: string_types
          :param attributes: 对象属性
          :return: 派生子类的实例
          :rtype: Object