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Swig with C++ and external libs

This is the kind of problem I work out how to solve, then I forget... and eventually have to do again... So more for my sake here is how to compile a python extension in c++ that has external libraries like opencv. Automatically wrapped with swig from distutils...

So first up I have a random library of C++ that I want to use from python. One such C file is doing some low level math on an opencv IPL image. Since I want to use this in python but require it to be fast, I need to create an extension.

// The header file I want to wrap.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include "cv.h"

void remove_corneal_reflection(IplImage *image, IplImage *threshold_image, int sx, int sy, int window_size,
     int biggest_crr, int &crx, int &cry, int& crr, int *valid_point_calc);


This has a few normal includes and "cv.h". This is refering to the opencv installed NOT in the default dir but in /usr/local/.

Next is the instructions for swig to use when creating the wrapper for the file. This uses the autodoc feature so in python the docstrings have some (almost) usefull information about what the parameters are.

/* Interface to the C file remove_corneal_reflection.c */
 
%module removeCornealReflection
%{
    /* Put header files here or function declarations like below */
    #include "opencv/cv.h"
    #include "remove_corneal_reflection.h"
 
%}
 
// Tell swig to put type information into the functions docstrings...
%feature("autodoc", "1");

// Tell swig to parse the header file.
%include "remove_corneal_reflection.h"

To get distutils to do all the compiling and linking we need a setup.py file:


import distutils
from distutils.core import setup, Extension
 
setup(
    name = "Brian's C++ Library wrapped up all nice for python",
    author = 'Brian Thorne',
    author_email = 'hardbyte@gmail.com',
    license='GPL v3 :: GNU General Public License',  
    version = "0.1",
    ext_modules = [
        Extension(
            "_helloWorld",
            sources = ["interfaceFile.i","Hello World.cpp"],
            swig_opts=["-c++"],
            ),
        Extension(
            "_removeCornealReflection",
            sources = ["remove_corneal_reflection.i","remove_corneal_reflection.cpp"],
            swig_opts=["-c++"],
            library_dirs=['/usr/local/lib/opencv'],
            libraries=['cv','highgui','cvaux','cvaux'],
            include_dirs = ['/usr/local/include/opencv']
            )
        ]
    )
And for the first time I also made a setup.cfg file with a whole two lines:

[build_ext]
inplace=1

And then the whole thing can be wrapped up with the familiar command:

brian@brian-hitlab:~/dev/swig/linkedLib$ python setup.py build
running build
running build_ext
building '_helloWorld' extension
swigging interfaceFile.i to interfaceFile_wrap.cpp
swig -python -c++ -o interfaceFile_wrap.cpp interfaceFile.i
creating build
creating build/temp.linux-x86_64-2.6
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c interfaceFile_wrap.cpp -o build/temp.linux-x86_64-2.6/interfaceFile_wrap.o
cc1plus: warning: command line option "-Wstrict-prototypes" is valid for Ada/C/ObjC but not for C++
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c Hello World.cpp -o build/temp.linux-x86_64-2.6/Hello World.o
cc1plus: warning: command line option "-Wstrict-prototypes" is valid for Ada/C/ObjC but not for C++
g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions build/temp.linux-x86_64-2.6/interfaceFile_wrap.o build/temp.linux-x86_64-2.6/Hello World.o -o _helloWorld.so
building '_removeCornealReflection' extension
swigging remove_corneal_reflection.i to remove_corneal_reflection_wrap.cpp
swig -python -c++ -o remove_corneal_reflection_wrap.cpp remove_corneal_reflection.i
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/opencv -I/usr/include/python2.6 -c remove_corneal_reflection_wrap.cpp -o build/temp.linux-x86_64-2.6/remove_corneal_reflection_wrap.o
cc1plus: warning: command line option "-Wstrict-prototypes" is valid for Ada/C/ObjC but not for C++
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/opencv -I/usr/include/python2.6 -c remove_corneal_reflection.cpp -o build/temp.linux-x86_64-2.6/remove_corneal_reflection.o
cc1plus: warning: command line option "-Wstrict-prototypes" is valid for Ada/C/ObjC but not for C++
g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions build/temp.linux-x86_64-2.6/remove_corneal_reflection_wrap.o build/temp.linux-x86_64-2.6/remove_corneal_reflection.o -L/usr/local/lib/opencv -lcv -lhighgui -lcvaux -lcvaux -o _removeCornealReflection.so


This creates two python extensions - one called helloWorld and one called removeCornealReflection. Ideal! Not sure why the warning message comes up, it looks like it is using gcc for the linking when surely g++ would be better... anyhow can't argue with positive results!

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