Sending a C++ array to Python and back (Extending C++ with Numpy)

Question

I am going to send a c++ array to a python function as numpy array and get back another numpy array. After consulting with numpy

Answer 1

We will be passing 2D array to python function written in file pyCode.py:

def pyArray (a):
    print ("Contents of a :")
    print (a)
    c = 0
    return c

1. For C++ to Python: File: c_code.cpp

#include 
#include 
#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
#include 

float Array [] = {1.2, 3.4, 5.6, 7.8};

int main (int argc, char *argv[])
{
    float *ptr = Array;
    PyObject *pName, *pModule, *pDict, *pFunc, *pArgs;
    npy_intp dims[1] = { 4 };
    PyObject *py_array;

    setenv("PYTHONPATH",".",1);
    Py_Initialize ();
    pName = PyUnicode_FromString ("pyCode");

    pModule = PyImport_Import(pName);

    pDict = PyModule_GetDict(pModule);

    import_array ();                                   

    py_array = PyArray_SimpleNewFromData(1, dims, NPY_FLOAT, ptr);
    

    pArgs = PyTuple_New (1);
    PyTuple_SetItem (pArgs, 0, py_array);

    pFunc = PyDict_GetItemString (pDict, (char*)"pyArray"); 

    if (PyCallable_Check (pFunc))
    {
        PyObject_CallObject(pFunc, pArgs);
    } else
    {
        cout << "Function is not callable !" << endl;
    }

    Py_DECREF(pName);
    Py_DECREF (py_array);                             
    Py_DECREF (pModule);
    Py_DECREF (pDict);
    Py_DECREF (pFunc);

    Py_Finalize ();                                    

    return 0;
}

compile the code: g++ -g -fPIC c_code.cpp -o runMe -lpython3.5m -I/usr/include/python3.5m/

2. From OpenCV Mat to Python:

file: cv_mat_code.cpp

#include 
#include 
#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
#include 

#include 

using namespace cv;
using namespace std;

int main (int argc, char *argv[])
{
    float data[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    Mat mat1 (cv::Size (5, 2), CV_32F, data, Mat::AUTO_STEP);
    int row = 0;
    float *p = mat1.ptr(row);

    cout << "Mat" << mat1 <

Compile the code: g++ -g -fPIC cv_mat_code.cpp -o runMe -lpython3.5m -I/usr/include/python3.5m/ -I/usr/include/ -lopencv_core -lopencv_imgproc -lopencv_highgui