[vtk-developers] Fixing VTK Python Installation

[Prabhu Ramachandran]

>>>>> "Brad" == Brad King <brad.king at kitware.com> writes:

    Brad> Prabhu, I've just committed changes that cause VTK libraries
    Brad> to be installed to PREFIX/lib instead of PREFIX/lib/vtk.
    Brad> The Tcl wrappers have been updated to be installed for the
    Brad> Tcl way of doing things.  Since there were no python install
    Brad> rules other than setup.py before I have left it unchanged,
    Brad> so it is probably broken.

Thanks for letting me know.  Can I go ahead change the
CMake/KitCommonBlock.cmake to use the Apple approach for Python?

    Brad> Now that the VTK libraries have versions and are installed
    Brad> in the proper place it is time to get the python install
    Brad> working as we discussed.  Do you have time to do this?  We
    Brad> are planning to branch 5.0 in the next week or two.

I will be in and out the next couple of weeks so will need a dashboard
buddy but can check in the changes.

    Brad> Here are a couple concerns I still have:

    Brad> 1.) If more than one version of VTK is installed (say 5.0
    Brad> and 5.2) how can the desired version be selected by python?
    Brad> In tcl one can write
[...]
    Brad> What is the python equivalent for this?  If everything goes
    Brad> in site-packages how can multiple versions be installed?

As Sander pointed out this is possible but I don't really like the
wxPython solution.  A more powerful, general and potentially widely
adopted solution to this problem is comming up via setuptools, Python
eggs and EasyInstall.  See here:

 http://peak.telecommunity.com/DevCenter/EasyInstall

My vote is to leave things simple right now so that everything works
for a single version of VTK (VTK-5.x).  I don't see the need to work
up a hurried solution at this time with a non-standard approach that
we will have to support in the future.

    Brad> 2.) I think running "make install" or building the INSTALL
    Brad> target should be all that is needed to install VTK.  It has
    Brad> already been built with a specific version of python so it
    Brad> needs to be installed in only one place.  We could provide a
    Brad> VTK_INSTALL_PYTHON_DIR cache entry that defaults to
    Brad> lib/python-<version>/site-packages and is settable by the
    Brad> user.  Then the main install target could install things
    Brad> directly to that location by automatically running a
    Brad> disutils-style setup.py configured to get things from the
    Brad> proper part of the build tree.

Alternatively, we could add a (fully documented)
VTK_PYTHON_SETUP_EXTRA_ARGS entry (in advanced?) where the user can do
whatever they want.  So in the INSTALL rule one simply has to do the
following:

  cd Wrapping/Python
  python setup.py install ${VTK_PYTHON_SETUP_EXTRA_ARGS}

    Brad> Is there any reason to require setup.py to be executed by
    Brad> the user after building?  I think if a setup.py is provided

Well, setup.py is useful to create a Python installer::

 python setup.py bdist_wininst

Under windows will create an exe file that the user can install.  In
the future this will be the approach to make Python eggs as well via:

 python setup.py bdist_egg

However, the person who needs to do this may easily do so from the
build directory.

    Brad> at all it should be in the source tree and it should know
    Brad> how to build and install VTK with python wrapping.  IIRC,
    Brad> that would be consistent with other python extension module
    Brad> sources.

Well, that looks like an incredibly complex task since we would have
to build all of VTK.  I think it is OK to just go with a default
INSTALL rule that does what most would expect.

Let me think about this more and wait for some comments from other
Python folks here.

Just as a data point.  When folks build wxPython from sources, this is
what they do:

 1. Get the sources for wxPython.  This bundles the wxWidgets sources
    as well, so this is similar to what VTK has.
 2. Read Robin Dunn's build instructions.
 3. Build wxWidgets with appropriate options.
 4. Install built wxWidgets.
 5. Build wxPython using installed wxWidgets via setup.py.
 6. Install wxPython also via setup.py.

This does take some work and is not meant for the average user.  Most
users just install binaries.

A VTK-Python build would go like this:

 1. Install CMake.
 2. Download VTK sources.
 3. Configure VTK.
 4. Build VTK.
 5. Install VTK.

If you know what you are doing you can use setup.py to do whatever
else is needed.  I'll try and document it in
Wrapping/Python/README.txt.

cheers,
prabhu