[vtkusers] VTK python wrapping issue -- collections

[tom fogal]

Hi all, I think I might have found a bug in the way
Actor(all?)Collections are passed between C++ and Python. I was hoping
someone had an idea for a workaround. Basically ActorCollections are
losing their Actors when being passed from Python -> C++.

Basically my setup is that: python is given a vtkDataSet. The script
then does whatever it wants, then eventually passes back a
vtkActorCollection with 1 or more actors in it.

This breaks down when python returns though. I suspect I am running
into a python-destruction (for lack of a better term) problem. The
ActorCollection is populated by Actors that are instantiated from
python. When PyObject_CallFunction(...) returns though, the Actors are
tagged (rightly, I suppose) as pure-python objects, and thus of course
to prevent memory leaks their memory must be reclaimed. However the
vtkActorCollection that I am getting back still references them.

It seems as if python also uses reference counting for memory
management. My guess is that even though vtkActorCollection has a
(python) reference count of 1 (since it must be returned to C++),
python has no way of knowing that Actors created in the python script
are referenced by the vtkActorCollection object; that is, the python
reference count of the actors becomes 0 while the vtk reference count
is still 1 (from the ActorCollection).

Could anybody confirm this? Even better, could somebody suggest a fix
or workaround?

-tom

BTW, I've noticed documentation on this subject is not so great. I
would be willing to (more) verbosely comment my current working source
and share it to contribute to the existing dearth, although I'm not
sure where to send it off to...