[Paraview-developers] addrofthis to give Python the address of a vtkObject

[Cory Quammen]

HI Axel,

> When looking through the source code of Paraview (from which we learn all the time for our own code), I found that to get the address of a vtkObject for Python interaction you use code like this:
>
>   // Set self to point to this
>   char addrofthis[1024];
>   sprintf(addrofthis, "%p", somepointer);
>   char *aplus = addrofthis;
>   if ((addrofthis[0] == '0') && ((addrofthis[1] == 'x') || addrofthis[1] == 'X'))
>     {
>     aplus += 2; //skip over "0x"
>     }
>   return std::string(aplus);
>
> However, sometimes you use aplus for referencing the address (e.g. in vtkPythonAnnotationFilter), but sometimes you use directly addrofthis, but still execute the part to compute aplus. This happens for example in vtkPythonView.cxx, line 142 ff.
>
> Since the first version is used a lot, is the second version in vtkPythonView.cxx a bug or does it serve a different purpose?

Hmm, you are right, that is different from other examples where the
object address is passed to Python, and is not intended. It seems to
work, though, or at least it did when I wrote the code.

My hunch is that the Python wrapping handles either case of passing
"0xffffffff" or "ffffffff" to the constructor to create a Python
object from an existing VTK object, but I don't know the Python
wrapping facilities well enough to verify that. Perhaps Python
wrapping guru David Gobbi can answer affirmatively.

> Also, this code snippet appears to be copied to quite a few places, but it is crucial for vtk Python interaction. Maybe a little static method in VTK could be created for that?

If the wrappers in fact do not handle both address formats, then yes
it would make sense to have a static member function that would do
this, probably in vtkPythonUtils.

Thanks,
Cory

> Thanks,
> Axel
>
>
> --
> Dr. Axel Gerstenberger
> Aero Methods and Design Systems Engineering (ET-DSE)
>
> Rolls-Royce Deutschland Ltd & Co KG
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-- 
Cory Quammen
R&D Engineer
Kitware, Inc.