def _bkwds(inst, Error=AttributeError, **n_v_s):
    """(INTERNAL) Set applicable C{bool} attributes.
    """
    for n, v in n_v_s.items():
        b = getattr(inst, n, None)
        if b is None:
            t = n, v, inst.__class__.__name__
            raise Error('not applicable: %s=%r for %s' % t)
        if v in (False, True) and v != b:
            setattr(inst, '_' + n, v)
