Call function from python with tuple return in c

Question

I'm trying to call a python function from my C script. I success to return a double variable from the python function and print it in my C script. The problem I have now is that I need to return multiple variables (tuple) from python. How can I success that? My code with a single variable return is as follows:

#include <python2.7/Python.h>

int main(){
PyObject *pName, *pModule, *pDict, *pFunc;
PyObject *pArgs, *pValue;   
int i;
double read;

Py_Initialize();
PyObject* sysPath = PySys_GetObject((char*)"path");
PyList_Append(sysPath, PyString_FromString("."));
pName = PyString_FromString("eadata"); //Primer posible error
pModule = PyImport_Import(pName);
Py_DECREF(pName);       

if(pModule != NULL){
    pFunc = PyObject_GetAttrString(pModule,"lectura");
    if(pFunc && PyCallable_Check(pFunc)){
        pValue = PyObject_CallObject(pFunc,NULL);
        if(pValue != NULL){
            printf("Result of call: %lf \n", PyFloat_AsDouble(pValue));
            Py_DECREF(pValue);
        }
        else{
            Py_DECREF(pFunc);
            Py_DECREF(pModule);
            PyErr_Print();
            fprintf(stderr,"Call failed\n");
            return 1;
        }
    }       
}
else{
    PyErr_Print();
    fprintf(stderr, "Error al cargar eadata.py \n");
    }
}

My python script is:

def lectura():

    device = '/dev/ttyUSB0'
    baudrate = 115200   
    mt=mtdevice1.MTDevice(device, baudrate)

    ax=mtdevice1.acx 
    ay=mtdevice1.acy
    az=mtdevice1.acz

    wx=mtdevice1.wx             
    wy=mtdevice1.wy
    wz=mtdevice1.wz

    mx=mtdevice1.mx
    my=mtdevice1.my
    mz=mtdevice1.mz

    roll = mtdevice1.roll
    pitch = mtdevice1.pitch
    yaw = mtdevice1.yaw
    pc = mtdevice1.pc

    return ax

This works, but I want to return other variables at the same time such as ay,az, and so on. Is my first time using embedded python and I really don't know how to do this.

Perhaps this discussion will provide a clue?

ryyker
– ryyker

2016-10-10 21:48:31 +00:00
Commented Oct 10, 2016 at 21:48 — ryyker
– ryyker, Commented Oct 10, 2016 at 21:48
Or this one

ryyker
– ryyker

2016-10-10 22:00:53 +00:00
Commented Oct 10, 2016 at 22:00 — ryyker
– ryyker, Commented Oct 10, 2016 at 22:00

Community · Accepted Answer · 2017-05-23 12:19:19Z

1

With a small caveat, you can use PyArg_ParseTuple to take apart the tuple returned by the function you call.

This will work fine as long as the returned tuple matches the format string you provide to PyArg_ParseTuple. If there is a mismatch, the error produced by PyArg_ParseTuple will be misleading because it assumes that the tuple is an argument tuple.

A less convenient but more general approach is to use the tuple API.

edited May 23, 2017 at 12:19

CommunityBot

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answered Oct 10, 2016 at 22:25

rici

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1 Comment

Juan Bravo Over a year ago

Yes. This works for me. I use the general approach tuple API. Thanks. @rici

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