'Fetch a QoS policy.
:param context: neutron api request context
:type context: neutron.context.Context
:param policy_id: the id of the QosPolicy to fetch
:type policy_id: str uuid
:returns: a QosPolicy object
:raises: n_exc.QosPolicyNotFound'

def _get_policy_obj(self, context, policy_id):

    obj = policy_object.QosPolicy.get_object(context, id=policy_id)
    if (obj is None):
        raise n_exc.QosPolicyNotFound(policy_id=policy_id)
    return obj
