Python C API doesn't load module

Question

I'm trying to load a python module that contains a math and numpy import in C, using the C API. I can load and run the module but, if I import the math module it doesn't work.

I'm using Arch Linux, Python 2.7.2 and gcc.

Here the codes:

#include <stdio.h>
#include <stdlib.h>
#include <python2.7/Python.h>
int main(int argc, char **argv)
{
 PyObject *pName, *pModule, *pFunc, *pArg, *pDict, *pReturn, *pT1, *pT2, *pX, *pY;
 int i;
 double x, y;
 Py_Initialize();
 PySys_SetPath(".");
 pName = PyString_FromString("func");
 if (!pName)
 {
 printf("pName\n");
 return 0;
 }
 pModule = PyImport_Import(pName);
 pDict = PyModule_GetDict(pModule);
 pFunc = PyDict_GetItemString(pDict, "get_vals");
 pArg = PyTuple_New(2);
 PyTuple_SetItem(pArg, 0, PyFloat_FromDouble(4.0));
 PyTuple_SetItem(pArg, 1, PyFloat_FromDouble(2.0));
 pReturn = PyObject_CallObject(pFunc, pArg);
 pT1 = PyTuple_GetItem(pReturn, 0);
 pT2 = PyTuple_GetItem(pReturn, 1);
 for (i = 0; i < PyTuple_Size(pT1); i++)
 {
 pX = PyTuple_GetItem(pT1, i);
 pY = PyTuple_GetItem(pT2, i);
 x = PyFloat_AsDouble(pX);
 y = PyFloat_AsDouble(pY);
 Py_XDECREF(pX);
 Py_XDECREF(pY);
 pX = NULL;
 pY = NULL;
 printf("Point p position is: %.2fx, %.2fy", x, y);
 }
 Py_XDECREF(pName); Py_XDECREF(pModule); Py_XDECREF(pFunc); Py_XDECREF(pArg); Py_XDECREF(pDict); Py_XDECREF(pReturn); Py_XDECREF(pT1); Py_XDECREF(pT2);
 Py_Finalize();
 return 0;
}

func.py

from math import cos
def get_vals(width, height):
 x = (1, 2)
 y = (cos(3), 4)
 return x, y

And how can I embbed the Python script to C without need to use the script?

• Janil: I got a segmentation fault after the program try to load the module... Now I'll try to use PyRun_SimpleString.

Answer 1

The PySys_SetPath(".") cleared the python path, so it could no longer find any library whatsoever. What you really need to do is import sys.path and then append your string to it:

PyObject *sys = PyImport_ImportModule("sys");
PyObject *path = PyObject_GetAttrString(sys, "path");
PyList_Append(path, PyString_FromString("."));

(I didn't test the above code, but it should be close. Also, you should do error checking)

• Santanor: I'm using Python 3.7 and PyString_FromString doesn't exist there. Took me a little bit but I thought somebody would find this helpful: Use PyUnicode_FromString
• TJez: You can also just append the path in the python language itself.