def add_to(self, parent, additions):
        for x in additions:
            if x not in parent:
                parent.append(x)
                self.changed()
A trigger should only be called on the first call to
dataset/ETHPy150Open smurfix/yapps/yapps/parsetree.py/Generator.add_to--crossover with--dataset/ETHPy150Open kuri65536/python-for-android/python-modules/twisted/twisted/test/test_internet.py/ThreePhaseEventTests.test_triggersRunOnce