[英]Passing arguments in Python function via C++
I am using a C++ program and I need to call Python objects from the C++ program (to perform optimization and mathematical operations). 我正在使用C ++程序,并且需要从C ++程序调用Python对象(以执行优化和数学运算)。 I am having trouble to pass arguments to Python object via C++ Here is a simple code
我无法通过C ++将参数传递给Python对象这是一个简单的代码
#include <Python.h>
#include <iostream>
#include <cstdio>
#include <cstdlib>
int main()
{
PyObject *pName, *pModule, *pDict, *pClass, *pInstance;
// Initialize the Python interpreter
Py_Initialize();
// Build the name object
pName = PyString_FromString("Adder");
// Load the module object
pModule = PyImport_Import(pName);
// pDict is a borrowed reference
pDict = PyModule_GetDict(pModule);
// Build the name of a callable class
pClass = PyDict_GetItemString(pDict, "Adder");
// Create an instance of the class
if (PyCallable_Check(pClass))
{
pInstance = PyObject_CallObject(pClass,NULL);
}
else
{
std::cout << "Cannot instantiate the Python class" << std::endl;
}
int sum = 0;
int x;
for (size_t i = 0 ; i < 5 ; i++)
{
x = rand() % 100;
sum += x;
PyObject_CallMethod(pInstance, "add","(i)",x);
}
PyObject_CallMethod(pInstance, "printSum", NULL);
std::cout << "the sum via C++ is " << sum << std::endl;
std::getchar();
Py_Finalize();
}
and the python class 和python类
class Adder:
# Constructor
def __init__(self):
self.sum = 0
# Add an element to the Adder
def add(self,x):
print "adding via python ", x
self.sum += x
# Print the total sum
def printSum(self):
print "the sum via the Python class is ",self.sum
Unfortunately, the argument x does not go through the python method add (when i call PyObject_CallMethod(pInstance, "add","i",x)) Calling the print method via python gives me "the sum via the Python class is 0". 不幸的是,参数x不能通过python方法add(当我调用PyObject_CallMethod(pInstance,“ add”,“ i”,x)时)通过python调用print方法使我“通过Python类的总和为0” 。 What is the best way to provide a number to a python method ?
向python方法提供数字的最佳方法是什么?
Thanks a lot for your help 非常感谢你的帮助
Vincent 文森特
PS : I defined a double add function in python as PS:我在python中定义了一个double add函数,
def add2(self,x,y):
print "double adding via python"
self.sum += x*y
Calling the following in C++ 在C ++中调用以下代码
PyObject_CallMethod(pInstance, "add2","(ii)",x,2);
is working... It seems that I have a problem with the format (i). 正在工作...似乎我的格式(i)有问题。
According to the docs of PyObject_CallMethod
, the format string should produce a tuple. 根据
PyObject_CallMethod
的文档 ,格式字符串应生成一个元组。 Also, don't ignore the return value. 另外,不要忽略返回值。 Try
尝试
PyObject *pValue;
pValue = PyObject_CallMethod(pInstance, "add","(i)",x);
if (pValue)
Py_DECREF(pValue);
else
PyErr_Print();
What worked for me was something like this python init and method: 对我有用的是这样的python init和方法:
class SwiftApi:
def __init__(self, user, key):
self.user = user
self.key = key
the python method python方法
def get_object(self, container, obj, resp_chunk_size=None,
query_string=None):
return 'some returned object here'
I was able to call the function from c++ code with this hack 我可以用这个hack从c ++代码中调用该函数
#include <python2.7/Python.h>
void error_abort(void)
{
PyErr_Print();
exit(EXIT_FAILURE);
}
int main (int argc, char *argv[])
{
PyObject *user, *key, *args, *md_module, *attr, *instance, *get_obj_tuple, *container, *obj,*methodcall,
Py_Initialize();
if (!(user = PyString_FromString("test:tester")))
error_abort();
if (!(key = PyString_FromString("testing")))
error_abort();
if (!(args = PyTuple_Pack(5,type, user, key, secret_key, authurl)))
error_abort();
PySys_SetPath("the path where the py file lives");
if (! (md_module = PyImport_ImportModule("SwiftApi")))
error_abort();
if (md_module != 0) {
printf ("got it middleware_module- %s\n", md_module);
}
else{ printf ("NO md_module ");}
if (!(attr = PyObject_GetAttrString(md_module, "ObjectStorageMiddleware")))
error_abort();
if (attr != 0) {
printf ("got the class- %s\n", attr);
}
if (!(instance = PyObject_CallObject(attr, args )))
error_abort();
if (instance != 0) {
printf ("###############got it ObjStrgRes instance - class- %d\n", (long)instance);
}
if (!(container = PyString_FromString("my-con-55")))
error_abort();
if (!(obj = PyString_FromString("ohad2.jpg")))
error_abort();
get_container_tuple = PyTuple_Pack(1, container);
get_obj_tuple = PyTuple_Pack(1, obj);
if (!(methodname = PyString_FromString("get_object")))
error_abort();
methodcall = PyObject_CallMethodObjArgs(instance, methodname, get_container_tuple, get_obj_tuple, NULL);
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