collision rays don’t stop after the first collision
they continue and collide with all collision nodes behind the first

if you comment out lines 74-77, smiley’s collision node is gone
no collisions will occur with it
i.e. collision nodes are important

if you uncomment line 57 the collision ray with collide with all
visible objects and therefore it will collide with smiley even
if his collision node is commented out
i.e. collision nodes are not needed

import direct.directbase.DirectStart
from direct.showbase import DirectObject #necessary for event handling
from pandac.PandaModules import *
from direct.gui.OnscreenText import OnscreenText
import sys #to exit on escape......sys.exit


class World(DirectObject.DirectObject):
    def __init__(self):
        #This code puts the standard title and instruction text on screen
        self.title = OnscreenText(
                            text="Panda3D: Tutorial - Mouse Picking",
                            style=1, fg=(1,1,1,1),
                            pos=(0.8,-0.95), 
                            align=TextNode.ACenter, scale = .07)
        self.escapeEvent = OnscreenText( 
                            text="ESC: Quit",
                            style=1, fg=(1,1,1,1), pos=(-1.3, 0.95),
                            align=TextNode.ALeft, scale = .05)
        self.mouse1Event = OnscreenText(
                            text="Left-click to pick an object",
                            style=1, fg=(1,1,1,1), pos=(-1.3, 0.90),
                            align=TextNode.ALeft, scale = .05)  
        self.onCollisionText = OnscreenText(
                            text="",
                            style=1, fg=(1,1,1,1), pos=(-1.3, 0.85),
                            align=TextNode.ALeft, scale = .05)  
                            
                                 
        #Escape quits 
        self.accept('escape', sys.exit)             
              
        #initialize traverser
        self.picker = CollisionTraverser()
        #initialize handler
        self.queue = CollisionHandlerQueue()

        #loading
        self.loadPicker()
        self.loadObj1()
        self.loadObj2()
        self.loadObj3()
 
        #waiting for the left mouse click
        self.accept("mouse1", self.collisionCheck)     
        
        
    def loadPicker(self):
        #attach a CollisionRay node to the camera
        self.pickerNode = CollisionNode('mouseRay')
        self.pickerNP = camera.attachNewNode(self.pickerNode)
        # self.pickerNode.setFromCollideMask(GeomNode.getDefaultCollideMask())
        self.pickerRay = CollisionRay()
        self.pickerNode.addSolid(self.pickerRay)
        self.pickerNP.show()    
        
        #add collision node (fromObject) to the traverser
        self.picker.addCollider(self.pickerNP, self.queue)
        self.picker.showCollisions(render)
        
    def loadObj1(self):

        #load a model. reparent it to the camera so we can move it.
        smiley = loader.loadModel('smiley')
        smiley.reparentTo(render)
        smiley.setPos(0, 25.5,0.5)
        
        #create a collision solid for this model
        cNode = CollisionNode('smiley')
        cNode.addSolid(CollisionSphere(0,0,0,1.1))
        smileyC = smiley.attachNewNode(cNode)
        smileyC.show()
        
    def loadObj2(self):      
        
        #load a model
        frowney = loader.loadModel('frowney')
        frowney.reparentTo(render)
        frowney.setPos(5, 25,0)
        
        #create a collsion solid for this model
        cNode = CollisionNode('frowney')
        cNode.addSolid(CollisionSphere(0,0,0,1.1))
        frowneyC = frowney.attachNewNode(cNode)
        frowneyC.show()
        
    def loadObj3(self):      
        
        #load a model
        frowney2 = loader.loadModel('frowney')
        frowney2.reparentTo(render)
        frowney2.setPos(5, 35,0.2)
        
        #create a collsion solid for this model
        cNode = CollisionNode('frowney22')
        cNode.addSolid(CollisionSphere(0,0,0,1.1))
        frowneyC = frowney2.attachNewNode(cNode)
        frowneyC.show()        
        
    def collisionCheck(self):
        if base.mouseWatcherNode.hasMouse():
            #get the mouse position
            mpos = base.mouseWatcherNode.getMouse()
            #aim the collision ray
            self.pickerRay.setFromLens(base.camNode, mpos.getX(), mpos.getY())
            #fire the ray and record, in the queue, any collisions 
            self.picker.traverse(render)
            
            if self.queue.getNumEntries() > 0:
                if self.queue.getNumEntries() == 1:
                    self.mytext = "A collision has occured with " \
                    + str(self.queue.getEntry(0).getIntoNodePath())  
                else:             
                    #organize the collisions from first hit to second...
                    self.queue.sortEntries() 
                    #output the name of the node paths the ray collided with
                    self.mytext = "A collision occured first with " \
                    + str(self.queue.getEntry(0).getIntoNodePath()) \
                    + " and then with " +  str(self.queue.getEntry(1).getIntoNodePath()) 
                               
                self.onCollisionText.setText(self.mytext)
                     
w = World()
run()

#note:  the collision ray doesn't stop after the first collision
#       it continues and collides with all collision nodes behind the first
#note:  if you comment out lines 74-77, smiley's collision node is gone
#       no collisions will occur with it
#note:  if you uncomment line 57 the collision ray with collide with all
#       visible objects and therefore it will collide with smiley even
#       if his collision node is commented out.i.e. collision nodes are
#       not needed

Ok, sorry for my stupidity, but i dont understand what you are accomplishing here.
With the following changes:

uncomented 58, 57 would have been wrong:

self.picker.addCollider(self.pickerNP, self.queue)

and comented 82-85:

        #cNode = CollisionNode('frowney')
        #cNode.addSolid(CollisionSphere(0,0,0,1.1))
        #frowneyC = frowney.attachNewNode(cNode)
        #frowneyC.show()

this returns, smiley, frowney22 and frowney, with frowney looking different because of lack of collision node. I can click on smiley, and frowney22, but frowney is just an object. the only difference is when frowney is in front of frowney22 that you cant click on frowney22, but this is expected. I may lack the information to understand, but how would this help if you do not have a response that frowney was picked. How would this be useful? How could you detect/determine which frowney was picked without a collision node?

Its been awhile since I played with the code and I’m away from my computer now so I’m just guessing here. I think I was talking about this line in the code:

self.pickerNode.setFromCollideMask(GeomNode.getDefaultCollideMask())

I was just playing around with the picking code. The picker can collide with geometry or a collision node. I was going to write up a follow up to this using tags but got side tracked.