Can't set edge.use_seam unless.. what, exactly?

I’m writing an addon that helps marking/clearing the seams on multiple objects at a time. The strange thing is that the code below works if I manually set some seams on the object(s) first, but not if the object has never had any seam on it. You can easily verify this by running it on on a newly created cube (won’t work) versus a cube where you already markes/cleared some seams on (will work).

def getAllEdges(meshObject):
    edgeList =[]
    for edge in 
    return edgeList

# ?? only works after manually setting a/some seam(s) first ??
def setSeams(edgeList, val):
    for edge in edgeList:
        edge.use_seam = val    

Am I missing something?

Well what the heck, here’s the addon – as it is ATM: (15.7 KB)

I’m not quite ready to release this yet, but since the above problem is hopefully the last thing standing in my way of doing so, you all can have a little sneak preview – so lucky you! :slight_smile: The code above can be found in, and it’s called from

This addon is about texturing multiple selected (usually generated and/or similar) objects. So we’ll be marking/clearing seams, unwrapping, and manipulating (normalizing, randomizing) their UV coordinates/maps. But let’s focus on setting the seams for now, though.

Please note that he addon will only appear (Misc tab on the tool shelf) if you have 1 or more meshes selected in your scene. I suggest you start with an empty scene, add a cube to it, and set the addon properties as follows:


Pressing the Action! button should mark all edges as seams, but when you go into edit mode, you’ll see no seams. If you select 1 edge and manually mark it as a seam, you’ll observe that all edges have now been marked as seams. You wouldn’t have observed that when you did not press the Action! button before. So… ?

Also, from now on (having manually marked a seam), the addon should work as expected. You can try marking/clearing, or even be a bit more precise about what edges you want to be affected.

So what gives? It seems like something is not being updated properly. Maybe this update could be requested/forced somehow?

TIA for any tips!