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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 create_or_update(cls, object_version, key, value):
 """Create or update a new tag for a given object version."""

        assert len(key) < 256
        assert len(value) < 256
        obj = cls.get(object_version, key)
        if obj:
            obj.value = value
            db.session.merge(obj)
        else:
            obj = cls.create(object_version, key, value)
        return obj