def _get_tolerance_line(line):
    """get a data item for a tolerance line with format (each line only one item):
    i: type=rel, 1e-3
    """
    assert line, 'Empty line!'
    line = line.strip().replace(' ','')
    stmp = line.split(':')
    key = stmp[0]
    _type, _val = stmp[1].split(',')
    _type = _type.split('=')[-1]
    tol={key:{'type':_type, 'val':float(_val)}}
    return tol