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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def start(self):
 """ Handle EventHub events for SmartContract decorators """

        self._events_to_write = []
        self._new_contracts_to_write = []

        @events.on(SmartContractEvent.CONTRACT_CREATED)
        @events.on(SmartContractEvent.CONTRACT_MIGRATED)
        def call_on_success_event(sc_event: SmartContractEvent):
            self.on_smart_contract_created(sc_event)

        @events.on(SmartContractEvent.RUNTIME_NOTIFY)
        def call_on_event(sc_event: NotifyEvent):
            self.on_smart_contract_event(sc_event)

        Blockchain.Default().PersistCompleted.on_change += self.on_persist_completed