...just to clarify on the (non-world) vertex thing...

What I would do is fetch them early on in the script and store them in your mymesh structure somewhere for future use.  After you're done fetching anything else for long-term use, just do a mesh.StructureChanged() and I'll free up my internal copy of those.

Since those are not needed or used by any other function in the .pyd file, they'll never get allocated again.  From that point forward, you're just moving the (world) vertices around, so mesh.VertPositionsChanged() is sufficient (when StructureChanged() is called, I delete all internal lists, when VertPositionsChanged() is called, I just set a 'dirty' flag on the relevent lists... in both cases the data will be re-fetched / re-generated if (and only if) it's called for again).

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