[vtk-developers] Python wrapping & factory methods

David Cole david.cole at kitware.com
Tue Apr 26 16:15:46 EDT 2011

I use the following regular expression in the ActiViz .NET C# wrappers to
determine what methods of VTK are "factory methods."


(seen in action in this file:

Perhaps I need to extend it to include CreateArray as well?

Does anybody know of any others?


On Tue, Apr 26, 2011 at 4:08 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Tim,
> All NewInstance() methods are wrapped the same way.  There isn't any
> hinting mechanism to tell the wrappers that a new instance is being
> created.  In fact the only way even a human programmer can tell is by
> reading the documentation.
> Since instance-creation methods are rare in VTK, I would be
> comfortable hard-coding the few that exist into the wrappers.  For
> instance, any method called NewInstance that returns an object can be
> assumed to return a new instance (because honestly, why else would a
> method have such a name?).
> As a temporary and very dirty fix, you can use SetReferenceCount() to
> avoid the memory leaks.
>  - David
> On Tue, Apr 26, 2011 at 1:39 PM, Timothy Shead <tshead at sandia.gov> wrote:
> >
> > I'm troubleshooting a reference-counting issue in the Python bindings for
> VTK - in a nutshell, the only way to instantiate vtkArray-derived classes
> from Python is through the vtkArray::CreateArray() static factory method
> (because vtkArray derivates are template classes).
> >
> > However, using vtkArray::CreateArray() from Python returns objects that
> have a reference-count of 2, because the Python wrapping code increments the
> reference-count of objects returned from "normal" class methods. This leads
> to annoying leaks when the program ends.
> >
> > From what I can see, there's a separate code path when instantiating VTK
> objects from Python.  I'm thinking that there must be other examples of
> factory methods in VTK, and that there must be some clean way of using them
> from Python?
> >
> > Thanks in advance,
> > Tim
> >
> >
> > --
> > Timothy M. Shead
> > Sandia National Laboratories
> > 1461, Scalable Analysis and Visualization
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