How to use the vivisect.const.LOC_OP function in vivisect

def getAllXrefsTo(vw, va):
    import vivisect
    #manually parse the preceding instruction & look to see if it can fall through to us
    #make a copy of the xrefs!!! or badness will ensue
    init = vw.getXrefsTo(va)[:]
    prev = vw.getPrevLocation(va)
    if prev is None:
        return init
    lva, lsize, ltype, linfo = prev
    if ltype != vivisect.const.LOC_OP:
        return init
    try:
        op = vw.parseOpcode(lva)
    except Exception:
        print ('Weird error while doing getAllXrefsTo: %s' % str(err))
        return init
    brlist = op.getBranches()
    for tova,bflags in brlist:
        if tova == va:
            init.append( (lva, tova, vivisect.const.REF_CODE, bflags) )
    return init

def get_prev_opcode(vw, va):
    prev_item = vw.getPrevLocation(va)
    if prev_item is None:
        raise RuntimeError('failed to find prev instruction for va: %x', va)

    lva, lsize, ltype, linfo = prev_item
    if ltype != vivisect.const.LOC_OP:
        raise RuntimeError('failed to find prev instruction for va: %x', va)

    try:
        op = vw.parseOpcode(lva)
    except Exception:
        logger.warning('failed to parse prev instruction for va: %x', va)
        raise

    return op