Python c++ wrapper : Convert multi-type struct to it's python representation (preferable dictionary)

Question

I've chosen setuptools to use my C/C++ code from python scripts. One of the phases when building such wrapper is to convert the C/C++ return value into python object.

So far I was able to convert simple primitive values and list of primitive values. However, I wish to extend it to multi-value struct, as shown in the example below.

My main challenge right now is how do I create the python struct representation (PyObject* ret = PyList_New(...);) and I do I set it's values properly with the different types.

I tried to create list of items from the same types (such as std::vector<float>) and manage to set the values properly using Py_BuildValue and PyList_SetItem, but I'm still struggling with the multi types...

typedef struct _fileParams 
{
    bool valid;
    int index;
    std::string key;
    std::value value;
} fileParams;

FileDataBase * db;

static PyObject *searchFileInDB(PyObject *self, PyObject *args)
{
    if (db == NULL) 
    {
        PyErr_SetString(PyExc_RuntimeError, "DB could not be initialized");
        return NULL;
    }

    char* fileName = NULL;
    int fileNameSize = 0;
    PyArg_ParseTuple(args, "s#", &fileName, &fileNameSize);
    try 
    {
        fileParams p;
        bool res = db->lookup(fileName, fileNameSize, p);
        PyObject* ret = PyList_New(...);

        if (res) 
        {                    
            PyObject* r1 = Py_BuildValue("b", p.valid);
            PyList_SetItem(ret, 0, r1);

            PyObject* r2 = Py_BuildValue("i", p.index);
            PyList_SetItem(ret, 1, r2);

            PyObject* r1 = Py_BuildValue("s", p.key);
            PyList_SetItem(ret, 2, r3);

            PyObject* r1 = Py_BuildValue("s", p.value);
            PyList_SetItem(ret, 3, r4);
        }
        return ret;
    } catch (...) {
        PyErr_SetString(PyExc_RuntimeError, "failed with C exception");
        return NULL;
    }
}

e.dan · Accepted Answer · 2018-11-18 12:26:42Z

1

You probably want to look into the Dictionary Object: Dictionary Objects

I'm guessing you'd want to set values with PyDict_SetItemString() as per that doc.

HTH

answered Nov 18, 2018 at 12:26

e.dan

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