

def exec_once(self, *args, **kw):
    'Execute this event, but only if it has not been\n        executed already for this collection.'
    if (not self._exec_once):
        with self._exec_once_mutex:
            if (not self._exec_once):
                try:
                    self(*args, **kw)
                finally:
                    self._exec_once = True

dataset/ETHPy150Open zzzeek/sqlalchemy/lib/sqlalchemy/event/attr.py _CompoundListener.exec_once/original