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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getVariantSet(self, id_):
 """ Returns the VariantSet with the specified name, or raises a VariantSetNotFoundException otherwise. """

        if id_ not in self._variantSetIdMap:
            raise exceptions.VariantSetNotFoundException(id_)
        return self._variantSetIdMap[id_]