layout shape migration

Hi All, i've written a simple script that grabs all shapes and changes the layerName and purpose as required (to map from one PDK to another). It works fine on small test cells. However i tried it out on a larger layout that has 52000 shapes (MPP's guard rings, looks llike each contact is a shape) & cadence crashes complaining of memory stack.

I think the code itself is efficient, but perhaps not:

foreach( shape_item cv~>shapes

 cond(
  (( nth( 0 shape_item~>lpp ) == "VTLN" && nth( 1 shape_item~>lpp )) == "drawing"
  shape_item~>layerName="OD" 
  shape_item~>purpose="drawing"
  )

nth( 0 shape_item~>lpp ) == "OD" && nth( 1 shape_item~>lpp )) == "drawing"

  shape_item~>layerName="NWELL" 
  shape_item~>purpose="drawing"
  )

...etc

 );end cond

);end foreach

So it sticks all the shapes in a list and then with the foreach it goes through each element of the list and change its layerName and purpose accordingly. If its not ok to have such a large list is it trivial to handle a list in say 500 elements at a time?

Or could it be that in layout land i am changing all these thousands of layer properties without a save and its too much data for the cadence to handle (or the undo stack becomes massive)?

Many thanks

Stu