[vtk-developers] Python wrapping & factory methods

[David Gobbi]

Hi David,

That's great, I can use the same list and centralize it so that it is
shared between the Python, Tcl, and Java wrappers.

This issue represents a significant oversight in the wrapper design.
Thanks for bringing this up, Tim.

 - David


On Tue, Apr 26, 2011 at 2:15 PM, David Cole <david.cole at kitware.com> wrote:
> I use the following regular expression in the ActiViz .NET C# wrappers to
> determine what methods of VTK are "factory methods."
>
>   "^(CreateImageReader2|CreateInstance|MakeTransform|New|NewInstance)$"
>
> (seen in action in this file:
> http://public.kitware.com/gitweb?p=activizdotnet.git;a=blob;f=MummySettings.xml.in;h=786b24431b7fc75749c1ebb16840757857cfff13;hb=HEAD
> )
>
> Perhaps I need to extend it to include CreateArray as well?
>
> Does anybody know of any others?
>
>
> HTH,
> David
>
>
> 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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