python: finding specific library version via CMake

[Michael Dickens]

In CMake, to find an exact required specific version, you can use EXACT
and REQUIRED, e.g:

  find_package(python 3.4.3 EXACT REQUIRED)

That said, the provided FindPython sucks, in that if multiple versions
of Python are installed it will generally find part in the
CMAKE_INSTALL_PREFIX and another part somewhere else. Mixing Python
executable and library -will- result in execution failure for any mixed
compiled language / Python script combo (e.g., SWIG, Boost Python).

I like Mark's version -much- better; something like what he's done has
been on my queue for a while now & I've just never had time to get to
it. Thanks, Mark! - MLD

On Wed, Jun 24, 2015, at 04:04 PM, Mark Moll wrote:
> Part of the problem is that there is no way to force the default CMake
> modules for finding an python interpreter and python libraries to agree
> on the same version. As a way around that I wrote my own
> FindPython.cmake:
> 
> https://bitbucket.org/ompl/ompl/src/tip/CMakeModules/FindPython.cmake
> 
> You can then specify a specific version:
> 
> 	find_package(python 3.4)
> 
> This will define PYTHON_EXEC, PYTHON_LIBRARIES, PYTHON_INCLUDE_DIRS,
> PYTHON_SITE_MODULES, and PYTHON_VERSION. If you run cmake like so:
> 
> 	cmake -DPYTHON_EXEC=/opt/local/bin/python3.4 ..
> 
> then the other variables are automatically defined appropriately.
> 
> You can also use it to find python modules:
> 
> 	find_python_module(numpy [version] [REQUIRED|QUIET])
> 
> Best,
> Mark
>
> > On Jun 22, 2015, at 4:01 PM, René J.V. Bertin <rjvbertin at gmail.com> wrote:
> > 
> > Hi,
> > 
> > I have a CMake file that has the following, hopefully self-explanatory, bit:
> > 
> > {{{
> > find_package(PythonLibs 3.4.3 REQUIRED)
> > if ( NOT ${PYTHONLIBS_FOUND} OR ${PYTHON_VERSION_MINOR} GREATER 4 )
> >    message(FATAL_ERROR "Python 3.4.3 with --enable-shared is required")
> > endif()
> > }}}
> > 
> > The only thing that did was picking up an old 2.4.3 (!) framework I'd installed as /Library/Frameworks/Python2.4.framework; after removing that it finds nothing at all.
> > I had a comparable issue with `find_package(PythonInterp 3.0 required)` which I could resolve by hardcoding the PYTHON_EXECUTABLE variable, but I don't think one can pull a similar trick with the PythonLibs script.
> > 
> > Is there a clean way out, I'm surely not the first one to try this?
> > 
> > Thanks,
> > R.