maya_uuid_on_save2.py

import maya.OpenMaya as om
import maya.cmds as mc
import uuid

def ensure_id(node):
    """Add a uuid attribute on the given node with a unique value.
    
    Skips nodes that already have the attribute, unless when used upon duplicating.
    
    Maya temporarily assigns the prefix '__PrenotatoPerDuplicare_' so we use that
    to lookup whether it's currently being duplicated.
    """
    node_attr = '{0}.uuid'.format(node)
    
    value = str(uuid.uuid4())
    
    if mc.objExists(node_attr):
        # When duplicating refresh the ID
        
        short_name = node.rsplit('|', 1)[-1]
        if short_name.startswith('__PrenotatoPerDuplicare_'):
            mc.setAttr(node_attr, lock=False)
            mc.setAttr(node_attr, value, type='string')
            mc.setAttr(node_attr, lock=True)
        return
    
    mc.addAttr(node, ln='uuid', dt='string')
    mc.setAttr(node_attr, value, type='string')
    mc.setAttr(node_attr, lock=True)


def callback(clientData):
    """Ensure ids on all non-referenced nodes"""
    nodes = mc.ls(long=True)
    nodes = [node for node in nodes if not mc.referenceQuery(node, isNodeReferenced=True)]
    
    for node in nodes:
        ensure_id(node)
    
    
if __name__ == '__main__':
    # Delete previous run (testing only)
    if 'id' in globals():
        try:
            om.MMessage.removeCallback(id)
        except RuntimeError, e:
            print e
            
    id = om.MSceneMessage.addCallback(om.MSceneMessage.kBeforeSave, callback)