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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 _set_update(self):
 """ Determine if we are creating a new stack or updating and existing one. The update member is set as you would expect at the end of this query. Args: None Returns: True """

        try:
            self._updateStack = False
            stack_name = self._config.get('environment', {}).get('stack_name', None)
            response = self._cloudFormation.describe_stacks(StackName=stack_name)
            stack = response['Stacks'][0]
            if stack['StackStatus'] == 'ROLLBACK_COMPLETE':
                logging.info('stack is in ROLLBACK_COMPLETE status and should be deleted')
                del_stack_resp = self._cloudFormation.delete_stack(StackName=stack_name)
                logging.info('delete started for stack: {}'.format(stack_name))
                logging.debug('delete_stack returned: {}'.format(json.dumps(del_stack_resp, indent=4)))
                stack_delete = self.poll_stack()
                if not stack_delete:
                    return False

            if stack['StackStatus'] in ['CREATE_COMPLETE', 'UPDATE_COMPLETE', 'UPDATE_ROLLBACK_COMPLETE']:
                self._updateStack = True
        except:
            self._updateStack = False

        logging.info('update_stack: ' + str(self._updateStack))
        return True