def once(self, event, *handlers):

        def _once_wrapper(*handlers):
            """wrapper for once decorator"""
            def _wrapper(*args, **kw):
                """call wrapper"""
                list(map(lambda x: x(*args, **kw), handlers))
                self.off(event, _wrapper)
            return _wrapper

        if handlers:
            return self.on(event, _once_wrapper(*handlers))
        return lambda x: self.on(event, _once_wrapper(x))
For any specified field, sort direction defaults to ascending.
dataset/ETHPy150Open timofurrer/pyobservable/observable/core.py/Observable.once--crossover with--dataset/ETHPy150Open mozilla/moztrap/tests/view/lists/test_sort.py/SortTest.test_default_direction