How to Extract a Python Function\'s Return Value When Called from C/C ?

Extracting Return Value from a Python Function Called in C/C

Calling a custom Python function from C/C allows for extended functionality, but extracting the return value can be challenging. Here's a solution using the Python C-API.

The Python Module

Create a Python module (mytest.py):

import math

def myabs(x):
    return math.fabs(x)

The C/C Code

Import the python3 interpreter in C/C (test.cpp):

#include <Python.h>

int main() {
    Py_Initialize();
    PyRun_SimpleString("import sys; sys.path.append('.')");

Importing and Calling the Function

1. Import the Python module:

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

2. Get a reference to the function:

PyObject* myFunction = PyObject_GetAttrString(myModule, "myabs");

3. Construct the function arguments:

PyObject* args = PyTuple_Pack(1, PyFloat_FromDouble(2.0));

4. Call the function:

PyObject* myResult = PyObject_CallObject(myFunction, args);

Extracting the Return Value

Convert the result to a double:

double result = PyFloat_AsDouble(myResult);

Usage

In your C/C code, you can now use the extracted return value (result):

printf("Absolute value: %f\n", result);

Note: Remember to check for any errors during these operations. For more details on the C-API, refer to the official documentation.

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