Calculate gid of a worksheet from its wid.

def wid_to_gid(wid):
    """Calculate gid of a worksheet from its wid."""
    widval = wid[1:] if len(wid) > 3 else wid
    xorval = 474 if len(wid) > 3 else 31578
    return str(int(widval, 36) ^ xorval)