code: def _set_update(self):
          
          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
docs: 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