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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 get_pk_values(cls, instance_or_pk):
 """Return a primary key as a tuple. :param instance_or_pk: An instance of this model class, or a primary key. A composite primary key can be passed as a tuple. """


        if isinstance(instance_or_pk, cls):
            cls._flask_signalbus_sa.session.flush()
            instance_or_pk = inspect(cls).primary_key_from_instance(instance_or_pk)
        return instance_or_pk if isinstance(instance_or_pk, tuple) else (instance_or_pk,)