Determine the priority range (min,max) for the given scheduler policy.

    If no policy is specified, the current default policy is used.

def _priority_range(policy=None):
    """Determine the priority range (min,max) for the given scheduler policy.

    If no policy is specified, the current default policy is used.
    """
    if policy is None:
        policy = libc.sched_getscheduler(0)
        if policy < 0:
            raise OSError(get_errno(),"sched_getscheduler")
    max = libc.sched_get_priority_max(policy)
    if max < 0:
        raise OSError(get_errno(),"sched_get_priority_max")
    min = libc.sched_get_priority_min(policy)
    if min < 0:
        raise OSError(get_errno(),"sched_get_priority_min")
    return (min,max)