Sometimes there will be situations where we need to pass data between CPP and Python codes. We can use Boost. Python to interface between CPP and Python. In this note, let’s see how to call CPP functions from Python and transfer Numpy arrays between them.

Test System Configuration

  • Ubuntu 20.04 LTS on WSL 1, Windows 10
  • Python 3.8
  • Boost 1.71 [To see Boost version, open up /usr/include/boost/version.hpp and look for #define BOOST_LIB_VERSION]

Install dependencies, if needed

  • sudo apt-get install libboost-all-dev
  • sudo apt install python-dev or sudo apt-get install python3-dev depending upon the Python
  • sudo apt install libboost-numpy-dev

Find out library names and their paths

We need the library names and their paths for linking.

  • Python - Find out where the pyconfig is [use find /usr/include/ -name pyconfig*]. In my system it was at /usr/include/python3.8/.
  • Boost Python - use find /usr/lib -name libboost*. In my system, boost_python library was at /usr/lib/x86_64-linux-gnu/libboost_python38. So the name of the library is boost_python38.
  • Boost Numpy - Just like Boost Python, I found out libboost_numpy was at /usr/lib/x86_64-linux-gnu/libboost_numpy38, and hence the library name was boost_numpy38


We need to create a shared library (.so) using Boost by compiling cpp code and linking existing libraries (boost_python, python, boost_numpy).

CPP header file - sample_interface.h

#include <boost/python.hpp>
#include <boost/python/extract.hpp>
#include <boost/python/stl_iterator.hpp>
#include <boost/python/numpy.hpp>

namespace np = boost::python::numpy;
namespace bpy = boost::python;

class SampleInterface{
    np::ndarray foo_bar(np::ndarray &input_array);
#endif // end of SAMPLE_INTERFACE

CPP definition file - sample_interface.cpp

#include "sample_interface.h" 
#include <iostream> 
using namespace std;


np::ndarray SampleInterface::foo_bar(np::ndarray &input_array){
    return input_array;

BOOST_PYTHON_MODULE(cpp_interface) { // cpp_interface should be name of .so file
    using namespace boost::python;
        .def("foo", &SampleInterface::foo_bar)

Generating shared library (.so) file

g++ sample_interface.cpp -I/usr/include/python3.8/ -lboost_python38 -lpython3.8 -lboost_numpy38 -fPIC --shared -o

Python file -

import numpy as np
import cpp_interface

arr = np.random.randint(1,10, size=(2, 3))
print("shape of input array:", arr.shape)
print("Input array:")

interface = cpp_interface.SampleInterface()
out_arr =
print("shape of array from cpp:", out_arr.shape)
print("Output array:")

All of these snippets are available here.