CODEWITHSUNDEEP
pythonc++opengllibraries
Alexander Kleinhans
Alexander Kleinhans

Reputation: 6258

Advice on creating Python libraries from C++?

I recently created a 3D and 2D force layout diagram visualizer in C++ using the OpenGL library (it uses some physics, sort of). Can someone give me some introductory pointers about making this useful as a Python library (issues or considerations and potential pitfalls I might run into)?

Upvotes: 4

Views: 183

Answers (2)

cyriel
cyriel

Reputation: 3532

While James Mills answer is fine, i would consider other option - use Boost.Python library to write python extensions. Here is a basic example. It looks like Boost.Python is not maintained (last update - 2009), but still it's a very good option. Right now i'm using it in one project and i've got to say that after a little difficult start, now it's really usefull and quite easy. Most important for me is that it handles reference counting(which is painful in Python/C API), allows to modify python objects inside c++ code and allows you to register converters for custom datatypes. So instead of writing:

MyClass test = convertPythonObjectToMyClass(pythonObject);
MyOtherClass test2 = convertPythonObjectMyOtherClass(pythonObject);

you can register your converters and than use this:

MyClass test = boost::python::extract<MyClass>(pythonObject);
MyOtherClass test2 = boost::python::extract<MyOtherClass>(pythonObject);

Of course you can consider other options as well - see this questions for more information about other solutions.

Upvotes: 0

James Mills
James Mills

Reputation: 19050

If I understand your question correctly you want to know how to write C extensions for use in Python. Here's a trivial simple example of how:

hello.c:

#include <Python.h>

static PyObject* helloworld(PyObject* self)
{
    return Py_BuildValue("s", "Hello, Python extensions!!");
}

static char helloworld_docs[] =
    "helloworld( ): Any message you want to put here!!\n";

static PyMethodDef helloworld_funcs[] = {
    {"helloworld", (PyCFunction)helloworld, 
     METH_NOARGS, helloworld_docs},
    {NULL}
};

void inithelloworld(void)
{
    Py_InitModule3("helloworld", helloworld_funcs,
                   "Extension module example!");
}

setup.py:

#!/usr/bin/env python

from setuptools import setup, Extension

setup(
    name='helloworld',
    version='1.0',
    ext_modules=[
        Extension('helloworld', ['hello.c'])
    ]
)

Build:

$ python setup.py develop
running develop
running egg_info
creating helloworld.egg-info
writing helloworld.egg-info/PKG-INFO
writing top-level names to helloworld.egg-info/top_level.txt
writing dependency_links to helloworld.egg-info/dependency_links.txt
writing manifest file 'helloworld.egg-info/SOURCES.txt'
reading manifest file 'helloworld.egg-info/SOURCES.txt'
writing manifest file 'helloworld.egg-info/SOURCES.txt'
running build_ext
building 'helloworld' extension
creating build
creating build/temp.linux-x86_64-2.7
x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c hello.c -o build/temp.linux-x86_64-2.7/hello.o
creating build/lib.linux-x86_64-2.7
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -D_FORTIFY_SOURCE=2 -g -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/hello.o -o build/lib.linux-x86_64-2.7/helloworld.so
copying build/lib.linux-x86_64-2.7/helloworld.so -> 
Creating /home/prologic/.virtualenvs/hellopyc/lib/python2.7/site-packages/helloworld.egg-link (link to .)
Adding helloworld 1.0 to easy-install.pth file

Installed /home/prologic/tmp/hello-py-c
Processing dependencies for helloworld==1.0
Finished processing dependencies for helloworld==1.0

Test:

$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import helloworld
>>> helloworld.helloworld()
'Hello, Python extensions!!'
>>>

Good luck!

Upvotes: 1

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