c++ - 将 python 与 C++ 集成

Question

我要整合python代码与 C++ ，其中c++源代码调用 python 中的函数/类.我特别需要从 c++ 传递数组代码到 python代码并从 python 获取另一个数组在 c++源代码。为了说明，main.cc

// call_function.c - A sample of calling 
// python functions from C code
// 

#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
#include <Python.h>
#include <iostream>
#include "numpy/arrayobject.h"


int main(int argc, char *argv[])
{
    PyObject *pName, *pModule, *pDict, *pFunc, *pValue, *pRet;

    const int SIZE{ 10 };
    npy_intp dims = SIZE;
    const int ND{ 1 };

    double* a = new double[10]();
    double* b = new double[10]();

    if (a == NULL)
    {
      exit(1);
    }
    std::cout << a[1] << std::endl;

    // Initialize the Python Interpreter
    Py_Initialize();
    import_array();
    PyRun_SimpleString("import sys\n");
    PyRun_SimpleString("sys.path.append(\"/home/mehdi\")");

    // Build the name object
    pName = PyUnicode_FromString("pytst");
    if (pName == NULL) exit(1);

    // Load the module object
    pModule = PyImport_Import(pName);
    if (pModule == NULL) exit(1);

    Py_DECREF(pName);
    if (!pModule){
        std::cout << "mymodule can not be imported" << std::endl;
        return 1;
    }

    // pDict is a borrowed reference 
    pDict = PyModule_GetDict(pModule);
    if (pDict == NULL) exit(1);

    PyObject *pArraya = PyArray_SimpleNewFromData(ND, &dims, NPY_DOUBLE, 
                                                  reinterpret_cast<void*>(a));

    import_array();

    PyArrayObject *np_arra = reinterpret_cast<PyArrayObject*>(pArraya);
    PyObject *pArrayb = PyArray_SimpleNewFromData(
        ND, &dims, NPY_LONGDOUBLE, reinterpret_cast<void*>(b));

    PyArrayObject *np_arrb = reinterpret_cast<PyArrayObject*>(pArrayb);
    if (!pArraya || !pArrayb)
        std::cout << "Error" << std::endl;


    // pFunc is also a borrowed reference 
    pFunc = PyDict_GetItemString(pDict, "multiply");

    if (PyCallable_Check(pFunc)) 
    {
        pRet = PyObject_CallObject(pFunc, pArraya);
    } else 
    {
        PyErr_Print();
    }

    if (!pRet)
        std::cout << "error" << std::endl;
    if (!PyArray_Check(pRet)) {
        std::cerr <<  " did not return an array." << std::endl;
    }


    if (pRet == NULL) exit(1);

    std::cout << 9 << std::endl;
    PyArrayObject *np_ret = reinterpret_cast<PyArrayObject*>(pRet);

    double* c_out;
    //int len = PyArray_SHAPE(np_ret)[0];
    std::cout << 10 << std::endl;

    c_out = reinterpret_cast<double*>(PyArray_DATA(np_ret));
    // Clean up
    Py_DECREF(pModule);
    Py_DECREF(pName);

    // Finish the Python Interpreter
    Py_Finalize();

    return 0;
}
}

pytst.py

import numpy as np
def multiply(a, b):
    c = np.array([])
    for i in range(10):
      c = np.append(c, a[i] + b[i])
    return c

并编译它我使用 g++ -Wall main.cc -o main -I/usr/include/python3.8 -I /usr/local/lib/python3.5/dist-packages/numpy/core/include .
我转换了 double*至 PyObject*转自 python至 c++ .但我得到 NULL为 pRet (将数组从 python 代码返回到 C++)。如果有人让我知道 c++ 之间的通信方式，我将不胜感激和 python代码发生。

Answer 1

Python 使用基于 PyObject 的变体类型来完成所有工作；您将需要创建表示包含 double 的列表的 PyObject 实例，例如

PyObject* alist = PyList_New(10);
for (i= 0;  i < 10;  i++)
{
    PyList_SetItem(alist, 0, PyFloat_FromDouble(a[i]));
}
...etc...

[编辑] 当您调用 Python 方法时，您需要将参数作为元组传递，例如:

PyObject* parameters = PyTuple_New(2); 
PyTuple_SetItem(parameters, 0, pArraya);
PyTuple_SetItem(parameters, 1, pArrayb);
pRet = PyObject_CallObject(pFunc, parameters);
Py_DECREF(parameters);

还可以查看一些在线示例，例如
https://gist.github.com/nad2000/9f69c5096e10c34acddb
我推荐使用 Cython，它比 CPython 好用得多，而且网上有很多教程。