Embedding Python in C

Question

I've been trying to run a Python 3 script through C using code the documentation provided.

main.c:

#include <stdio.h>
#include <stdlib.h>
#include <Python.h>
/*
 * 
 */
int main(int argc, char** argv) {
 PyObject *pName, *pModule, *pDict, *pFunc;
 PyObject *pArgs, *pValue;
 int i;
 if (argc < 3) {
 fprintf(stderr,"Usage: call pythonfile funcname [args]\n");
 return 1;
 }
 Py_Initialize();
 pName = PyUnicode_FromString(argv[1]);
 /* Error checking of pName left out */
 pModule = PyImport_Import(pName);
 Py_DECREF(pName);
 if (pModule != NULL) {
 pFunc = PyObject_GetAttrString(pModule, argv[2]);
 /* pFunc is a new reference */
 if (pFunc && PyCallable_Check(pFunc)) {
 pArgs = PyTuple_New(argc - 3);
 for (i = 0; i < argc - 3; ++i) {
 pValue = PyLong_FromLong(atoi(argv[i + 3]));
 if (!pValue) {
 Py_DECREF(pArgs);
 Py_DECREF(pModule);
 fprintf(stderr, "Cannot convert argument\n");
 return 1;
 }
 /* pValue reference stolen here: */
 PyTuple_SetItem(pArgs, i, pValue);
 }
 pValue = PyObject_CallObject(pFunc, pArgs);
 Py_DECREF(pArgs);
 if (pValue != NULL) {
 printf("Result of call: %ld\n", PyLong_AsLong(pValue));
 Py_DECREF(pValue);
 }
 else {
 Py_DECREF(pFunc);
 Py_DECREF(pModule);
 PyErr_Print();
 fprintf(stderr,"Call failed\n");
 return 1;
 }
 }
 else {
 if (PyErr_Occurred())
 PyErr_Print();
 fprintf(stderr, "Cannot find function \"%s\"\n", argv[2]);
 }
 Py_XDECREF(pFunc);
 Py_DECREF(pModule);
 }
 else {
 PyErr_Print();
 fprintf(stderr, "Failed to load \"%s\"\n", argv[1]);
 return 1;
 }
 Py_Finalize();
 return 0;
}

test.py:

def multiply(a,b):
 print("Will compute", a, "times", b)
 c = 0
 for i in range(0, a):
 c = c + b
 return c

I enter into the console:

./pytest test multiply 3 4

and I get:

AttributeError: 'module' object has no attribute 'multiply'
Cannot find function "multiply"

I'm using Ubuntu 13.10; I figured this was relevant because the documentation appeared to be addressing Windows. What am I missing?

Answer 1

You've forgotten (or rather, were never told) that the current/script/executable directory is not added to sys.path when embedding the interpreter, so you've found some completely different module called "test" and are importing that instead.

• user1610810: Thanks a bunch I'll keep this in mind in the future. Since I still have your attention, I've renamed the file to "qwe.py" and now I get ImportError: No module named 'qwe' Failed to load "qwe"
• user1610810: Never mind I'm headed towards the right direction now. Thanks again.
• Ignacio Vazquez-Abrams: @user1610810: The problem isn't that it found some other module instead of yours, it's that it isn't capable of finding yours in the first place.
• user1610810: I figured that. I tried making it reachable using PySys_SetPath(PyBytes_FromString("/home/frosty/NetBeansProjects/pyTest/")); , but no luck. Is there documentation I can just dive into?
• Ignacio Vazquez-Abrams: @user1610810: No, there is none. You can manipulate sys.path as you would any other list though.