Exiting a Python script

[user_deleted]

I am writing a script that a user triggers by selecting an item in a menu.  First, the script must check if any nodes are selected, so I wrote this code:

selectedNodes = nuke.selectedNodes()

if len(selectedNodes) == 0:
    msg = 'No nodes selected.'      
    nuke.message(msg)

If no nodes were selected, the script should flash a message and exit after the user clicks the 'OK' button.  I am trying to figure out how to do this.  According to the docs, nuke.scriptExit() exits Nuke, which I do not want.  I tried using nuke.scriptClose(), which caused Nuke to exit and realaunch!  I then used sys.exit(), which caused Nuke to exit.  Any hints?