Read the default class processors if none have been set.

def get_processors(self):
        "Read the default class processors if none have been set."
        procs_x,procs_y = listify(self.train.x._processor),listify(self.train.y._processor)
        xp = ifnone(self.train.x.processor, [p(ds=self.train.x) for p in procs_x])
        yp = ifnone(self.train.y.processor, [p(ds=self.train.y) for p in procs_y])
        return xp,yp