def _SI(size, K=1024, i='i'):
    """Return size as SI string.
    """
    if 1 < K <= size:
        f = float(size)
        for si in iter('KMGPTE'):
            f /= K
            if f < K:
                return ' or %.1f %s%sB' % (f, si, i)
    return ''
