[vtk-developers] Python wrapping & factory methods

[Michael Halle]

A longer-term alternative could be a wrapper generation decorator for factory methods that could live in the .h file.

--Mike




On Apr 26, 2011, at 4:23 PM, David Gobbi wrote:

> 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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