Writing to derived/deformed vectors?

Coding Python Support
1

Hello, does anyone know how to write to a “derived/deformed vector”, namely a vector which is the slurph of vectors from shape keys? I can read them as mesh data, but I can’t figure out how to write to them. I have the classic problem of needing to modify deformed vectors because at certain shape key values the vectors exceed desired boundaries. I would like to move the vectors to keep them in bounds.
I found the following in the blender source code module Derived Mesh.c - mesh_calc_modifiers routine:

/* Result of all leading deforming modifiers is cached for
   * places that wish to use the original mesh but with deformed
   * coordinates (vpaint, etc.)
   */

Sure enough, the modified coordinates can be seen in the mesh data but I can’t figure out how to modify them.
BTW: When not using shape keys, I’m able to modify the mesh data directly.
Any assistance is appreciated!!

2

You cant write to derived mesh data at the moment, to do this youd either need to convert into a mesh and modify or have ‘python modifiers’

3

Bummer… I thought about ‘hiding’ the original mesh w/ shape keys on a non-displayed layer, copying the modified mesh data, and creating a new static mesh from that data onto a visible layer. Little bit of overhead, but time isn’t a huge factor. Everything is currently being done in Python.
What is a python modifier?
This simple test code works with static meshes but as you said, it does not work with shape key based meshes:

 obj          = Blender.Object.GetSelected()[0]
 mesh         = obj.getData(mesh=1)  
 
 for vertNum in xrange(len(mesh.verts)):
  mesh.verts[vertNum].co = Vector(0,0,0)
 
 mesh.update()

BTW: One can view some of my work on youtube under username screamatthewind