'Step task runner. No try..except needed due to defer wrap.'

def _step_callback(self):

    if (not self.is_valid()):
        self.stop()
        return
    self.at_repeat()
    callcount = self.ndb._task.callcount
    maxcount = self.db_repeats
    if ((maxcount > 0) and (maxcount <= callcount)):
        self.stop()
