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# callback basedclass BatchProcess(Item):    def processIt(self):        chain = RunChain(store=self.store, initialStep=self)        chain.addStep(BatchStep1(store=self.store))        chain.addStep(BatchStep2(store=self.store))# state basedclass BatchProcess(Item):    step = integer(step=0)    def drive(self):        self.step += 1        getattr(self, "step_%d")()    def step_1(self):        ...    def step_2(self):        ...