Houdini Isolate Select

import os
def isolate():
    sel = hou.selectedNodes()
    if not sel:
        sel_string = "*"
    else:
        sel_string = " ".join([n.name() for n in sel])
    try:
        if hou.os.environ['CUR_ISOLATE'] == sel_string:
            sel_string = "*"
    except: pass
    hou.hscript('viewdisplay -G "%s" `run("viewls -n")`' % sel_string)
    os.environ['CUR_ISOLATE'] = sel_string