new_contents: class classproperty(property):
      """
      A decorator that behaves like @property except that operates
      on classes rather than instances.
  
      Original Implementation: sqlalchemy.util.langhelpers.classproperty
      """
  
      def __init__(self, fget, *arg, **kw):
          super(classproperty, self).__init__(fget, *arg, **kw)
          self.__doc__ = fget.__doc__
  
      def __get__(desc, self, cls):
          return desc.fget(cls)
  
subject: add classproperty