Object don't working

class PlansScreen(Screen):

    def set_class_nr(self,x):
        x = str(x)
        self.class_nr = x

    def get_class_nr(self):
        return self.class_nr

    def show_plan(self,nr):
        self.set_class_nr(nr)
        self.manager.current = 'currentplan'

    pass

class CurrentPlanScreen(Screen):

    def refresh_plan(self):
        name = "Plans/"+str(self.class_nr)+str(self.day_nr)+".txt"
        self.ids.planhere.text = name

    def set_day_nr(self,x):
        x = int(x)
        self.day_nr = x
        self.refresh_plan()

    pass