C++如何調(diào)用python并取返回值

更新時間：2024年03月01日 10:53:01 作者：玖五二七

這篇文章主要介紹了C++如何調(diào)用python并取返回值問題,具有很好的參考價值,希望對大家有所幫助,如有錯誤或未考慮完全的地方,望不吝賜教

C++調(diào)用python并取返回值

前面介紹了用python調(diào)用C++時用swig工具，現(xiàn)在簡單介紹一下C++調(diào)用python并取返回值的過程

python文件test.py

class tester:
    def add(self, a, b):
        return a + b

新建一個VS控制臺項目

main.cpp所有的源碼如下:

#include <stdio.h>
#include <python.h>
#include <windows.h>
void main()
{
    Py_Initialize(); // 初始化python虛擬機
    PyObject* pyMod  = PyImport_ImportModule("test"); //  加載test.py文件
    PyObject* pyDict = PyModule_GetDict(pyMod); //  獲取test模塊中的字典
    PyObject* pyCls = PyDict_GetItemString(pyDict, "tester"); // 從字典中查找tester類
    PyObject* PyIns = PyInstance_New(pyCls, NULL, NULL); // 創(chuàng)建tester類
    PyObject* pyRet = PyObject_CallMethod(pyIns, "add", "ii", 5, 6); // 調(diào)用tester.add方法，傳入2個int型參數(shù)
    int ok = -1;
    int retok = PyArg_Parse(pyRet, "i", &ok); // 從返回值從取出int型返回值
    Py_Finalize();
    system("pause");
}

整個過程最重要的是 PyBoject_CallMethod，傳入的參數(shù)類型一定不能搞錯。

還有取返回值的時候PyArg_Parse取單個返回值，要是取多個的可以用PyArg_ParseTuple，要取的類型也必須完全匹配。

c++調(diào)用python時參數(shù)傳遞和返回值解析

通過python接口在cpp中調(diào)用python函數(shù)時，構建傳參和解析返回值都會用到python內(nèi)的變量類型和c++的變量類型之間的轉(zhuǎn)換。

返回值是numpy等復雜結構的數(shù)據(jù)時，可以通過先轉(zhuǎn)換為list等類型再返回，或者單獨構建一個函數(shù)，獲取numpy內(nèi)某個位置的變量的函數(shù)。

下面幾個基礎類型的返回值解析

#python
#返回一個參數(shù)
def returnInt(a,b):
    return a+b
#返回兩個相同類型的參數(shù)
def returnTwoInt():
    return 1,2
#返回字符串
def returnString():
    srt = 'hello world'
    return srt
#返回list
def returnList():
	para = [1, 2, 3, 4]
    return 1,para.tolist()
#返回兩個不同類型的參數(shù)
def returnTwo():
	para = [1, 2, 3, 4]
    return 1,para.tolist()
#返回矩陣
def returnMat():
    img = cv2.imread('test1.bmp',cv2.IMREAD_GRAYSCALE)
    return img

	//調(diào)用python函數(shù)，返回的數(shù)據(jù)統(tǒng)一為PyObject類型，需要根據(jù)實際類型進行解析
	PyObject* pReturn = PyObject_CallObject(pFunc, pArgs);
	//當不需要傳參時，可以將參數(shù)位置為空
	PyObject* pReturn = PyObject_CallObject(pFunc,NULL);

PyObject為結構體，參數(shù)ob_type->tp_name 為數(shù)據(jù)的類型

//不同類型參數(shù)傳遞
	PyObject* p = PyTuple_New(4);
	for (int i = 0; i < 4; i++)
		PyTuple_SetItem(p, i, Py_BuildValue("i", i));
	PyObject* pArgs = PyTuple_New(2);
	PyTuple_SetItem(pArgs, 0,Py_BuildValue ("i",1));
	PyTuple_SetItem(pArgs, 0,Py_BuildValue ("O",p));
	
//返回為list
	double temp;
	int i_size = PyList_Size(pReturn); 
	for (int i = 0; i < i_size; ++i)
	{
		PyArg_Parse(PyList_GetItem(pReturn, i), "d", &temp);
		std::cout << "return result is " << (temp) << std::endl;
	}
//返回為 int 和 list 兩個不同類型的參數(shù)
	PyArg_Parse(PyTuple_GetItem(pReturn, 0), "d", &temp);
	std::cout << "temp is " << (temp) << std::endl;
	PyObject* pReturnlist;
	PyArg_Parse(PyTuple_GetItem(pReturn, 1), "O", &pReturnlist);
	i_size = PyList_Size(pReturnli); 
	for (int i = 0; i < i_size; ++i)
	{
		PyArg_Parse(PyList_GetItem(pReturnli, i), "d", &temp);
		std::cout << "return result is " << (temp) << std::endl;
	}
//返回單獨一個變量
	//構建輸入
	PyObject* pArgs = PyTuple_New(2);
	PyTuple_SetItem(pArgs, 0, Py_BuildValue("i", 1));
	PyTuple_SetItem(pArgs, 1, Py_BuildValue("i", 1));
	PyObject* pReturn2 = PyObject_CallObject(pFunc, pArgs);
	//解析
	int nResult1;	//解析為int
	PyArg_Parse(pReturn2, "i", &nResult1);
	std::cout << "add=" << nResult1 << std::endl;
	double nResultd;	//解析為double
	PyArg_Parse(pReturn2, "d", &nResultd);
	std::cout << "add=" << nResultd << std::endl;
//返回字符串
	//解析方法1：
	PyObject* repr = PyObject_Repr(pReturn);
	PyObject* str = PyUnicode_AsEncodedString(repr, "utf-8", "strict");
	char* result = PyBytes_AsString(str);
	std::cout << result << std::endl;
	//解析方法2：
	char* pstr = NULL;
	PyArg_Parse(pReturn, "s", &pstr);
	std::cout << pstr << std::endl;

//返回多個變量
	//循環(huán)解析
	int nResult;
	i_size = PyTuple_Size(pReturn); 
	for (int i = 0; i < i_size; ++i)
	{
		PyArg_Parse(PyTuple_GetItem(pReturn, i), "i", &nResult);
		std::cout << "return result is " << (nResult) << std::endl;
	}
	//直接解析
	int nResult1;
	int nResult2;
	PyArg_ParseTuple(pReturn,"i|i", &nResult1, &nResult2);   
	std::cout << "return  " << nResult5<< ' ' << nResult6 << std::endl;
//解析二維矩陣
	//獲得序列長度，即行數(shù)
	Py_ssize_t rsize = PyObject_Size(pReturn);
	std::cout << rsize << std::endl;
	//轉(zhuǎn)換到迭代器，用于提取數(shù)據(jù)
	PyObject* iter = PyObject_GetIter(pReturn5);
	while (true)
	{
		//獲取矩陣的第一行
		PyObject* next = PyIter_Next(iter);
		if (!next) { // nothing left in the iterator
			break;
		}
		if (!PyList_Check(next))
		{ // error, we were expecting a list value }
		//獲得當前行的數(shù)據(jù)數(shù)量
		Py_ssize_t foosize = PyObject_Size(next);
		std::cout << foosize << std::endl;
		//轉(zhuǎn)換到迭代器，用于獲取數(shù)據(jù)
		PyObject* iter2 = PyObject_GetIter(next);
		while (true)
		{
			PyObject* next2 = PyIter_Next(iter2);
			if (!next2)
				break;
			if (!PyFloat_Check(next2))
			 {// error, we were expecting a floating point value}
			double foo = PyFloat_AsDouble(next2);
			std::cout << foo << " ";
		}
		std::cout << std::endl;
	}

python手冊，接口的使用示例等

https://docs.python.org/3/

	//解析常用字段：
	// b <=>char 0-255的那個char
	// c <=>char 單個字符
	// h <=>short int
	// l <=>long int
	// f <=>float
	// d <=>double
	// s <=>char*
	// O <=> PyObject