def __set__(self, instance, value):
        if instance is None:
            raise AttributeError("Manager must be accessed via instance")

        if not self.field.rel.through._meta.auto_created:
            opts = self.field.rel.through._meta
            raise AttributeError("Cannot set values on a ManyToManyField which specifies an intermediary model.  Use %s.%s's Manager instead." % (opts.app_label, opts.object_name))

        manager = self.__get__(instance)
        manager.clear()
        manager.add(*value)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/db/models/fields/related.py/ReverseManyRelatedObjectsDescriptor.__set__/original