[CMake] How to install openbabel python bindings by using the new cmake installer (problem selecting a particular python version).

[Marcus D. Hanwell]

On Nov 13, 2010, at 8:57 AM, Michael Hertling wrote:

> On 11/12/2010 02:13 PM, Hector Martinez-Seara wrote:
>> Dear all,
>> I'm trying to install openbabel in linux which in its last version
>> (2.3.0) uses cmake installer. I haven't been able to compile it with
>> biddings with python 3.1 when using the -DPYTHON_BINDINGS=ON option. I
>> have python 2.7 and 3.1 installed in my system and the python command
>> points to python 3.1. Still cmake only select python 2.7 despite it is
>> not set as preferred in my system in any way. I have made a small
>> search and I have seen that there is a lot of troubles selecting
>> python 3 with cmake. Most of the information was very technical and
>> honestly I'm not sure if there was any solution at the end.
> 
> AFAIK, the FindPython{Interp,Libs}.cmake modules are currently not
> capable to find Python 3, so you should focus on a manual approach
> at the moment, see below. With the scheduling of issue 8396 for the
> 2.8.4 roadmap, there's a perpective for the availability of version-
> or pattern-aware find functions, so maybe, it is possible to improve
> the find modules w.r.t. version selection in the near or medium term.

This is certainly something I would like to address before the 2.8.4 release, but as you said there is no Python 3 awareness right now in the find modules. Do the Open Babel Python modules work in Python 3? I work on that project, and was not aware that Python 3 support was there, but do not work much on the bindings.
> 
>> My question is rather easy:
>> a) Is there any way to force a specific python version (3.1) from the
>> cmake command line?
> 
> You might try to set the PYTHON_EXECUTABLE, PYTHON_INCLUDE_DIR and
> PYTHON_LIBRARY variables to appropriate values for your Python 3.1
> installation on the command line, i.e. by use of the -D option or
> -C along with a prepared script. AFAICS, defining these variables
> makes the FindPython{Interp,Libs}.cmake modules not look for the
> interpreter, the include directory and the library by themselves,
> so you possibly get by without any further modifications, but I
> have not yet tested this with Open Babel.
> 
>> or b) Is there variable which I could export, e.g. CC=gcc4.5, to force
>> python to select the python version I want?
> 
> None I'm aware of, but - as stated above - there're some undertakings
> in the near future that might result in a comprehensive and flexible
> FindPython.cmake module which receives the requested version through
> FIND_PACKAGE()'s version parameter, including version 3.
> 
That would certainly be the ideal solution.

Marcus