def exec_once(self, *args, **kw):

        if not self._exec_once:
            with self._exec_once_mutex:
                if not self._exec_once:
                    try:
                        self(*args, **kw)
                    finally:
                        self._exec_once = True
:return: a verbose string representation of this
dataset/ETHPy150Open zzzeek/sqlalchemy/lib/sqlalchemy/event/attr.py/_CompoundListener.exec_once--crossover with--dataset/ETHPy150Open nltk/nltk/nltk/chunk/regexp.py/RegexpParser.__str__