[vtkusers] Status of VTK Python 3 wrapper support

[Berk Geveci]

Hi David and others,

I don't think that this workflow would work for us. Most of our
collaborators, specially in the supercomputing community, are going to take
a while longer to move to Python 3. So as a team, we need to continue to do
our day-to-day work using Python 2. So having to go through a 3-to-2
conversion mechanism would be very cumbersome. We would have to regularly
maintain 2 builds, do the development in 3 then move to the 2 build, test
etc.

I suggest taking smaller steps. Starting with porting of the core modules
(not the tests) and seeing what will be involved in maintaining both 2 and
3 versions (or a 2-to-3 conversion on the fly) would be my suggestion. Once
we can demonstrate the maintainability of this, I suspect that doing a
2-to-3 conversion on the fly for the tests would be pretty easy.

Best,
-berk


On Thu, Jul 31, 2014 at 4:15 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> On Thu, Jul 31, 2014 at 6:44 AM, diego0020 <da.angulo39 at uniandes.edu.co>
> wrote:
> >
> > But I am also looking forward to this. Is there anything we could do to
> push
> > support for python 3 forward?
>
> There has been some discussion about converting all of the python
> tests and examples, which is a part of the process where extra
> manpower would be a big asset.  I imagine that the conversion will
> go something like this:
>
> 1) Someone will run 2to3 on all the python code, and then make
> sure that it can be byte-compiled with python3 (it will be too early
> at this stage to actually run the code, but making sure that it
> byte-compiles will be a good first step).
>
> 2) Lots of people will then pick through the code to fix conversion
> errors and to make sure that the code actually looks like good
> python3 code.
>
> 3) Finally, someone will add some CMake magic to VTK so that if VTK
> is built against python2, cmake will run 3to2 on all of these new python3
> files and put the equivalent python2 code into the VTK build
> directory.  This is the magic that is needed to make sure that VTK
> will be able to support both python2 and python3.
>
> So any assistance with the above process would be a big help.  In
> particular, it would be very useful if someone could verify that item
> (3) is even feasible: in the end it might be necessary to have hand-
> written python2 and python3 exist side-by-side instead of using
> automatic conversion.  It _should_ be feasible, since the VTK
> tests used automated tcl-to-python conversion for many years,
> and python3 to python2 should be much easier than tcl to python.
>
>  - David
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