Calling a python method from C/C++, and extracting its return value

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As explained before, using PyRun_SimpleString seems to be a bad idea.

You should definitely use the methods provided by the C-API (http://docs.python.org/c-api/).

Reading the introduction is the first thing to do to understand the way it works.

First, you have to learn about PyObject that is the basic object for the C API. It can represent any kind of python basic types (string, float, int,…).

Many functions exist to convert for example python string to char* or PyFloat to double.

First, import your module :

PyObject* myModuleString = PyString_FromString((char*)"mytest");
PyObject* myModule = PyImport_Import(myModuleString);

Then getting a reference to your function :

PyObject* myFunction = PyObject_GetAttrString(myModule,(char*)"myabs");
PyObject* args = PyTuple_Pack(1,PyFloat_FromDouble(2.0));

Then getting your result :

PyObject* myResult = PyObject_CallObject(myFunction, args)

And getting back to a double :

double result = PyFloat_AsDouble(myResult);

You should obviously check the errors (cf. link given by Mark Tolonen).

If you have any question, don’t hesitate. Good luck.

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