Python uses NotImplementedError exactly for the purpose of signaling the method should be overriden by the subclass. And code with almost complete, but not rea

Python uses NotImplementedError exactly for the purpose of signaling the method should be overriden by the subclass. And code with almost complete, but not really, interface (i.e. with several methods lacking) looks awful. I would say it's an error on the Ruby language developers' side not to provide means to signal the method needs to be overriden.