intercalar.c

#include <Python.h>

/* Compilando:
 * gcc -Wall -shared -fPIC -o intercalar.so intercalar.c -I /usr/include/python2.7
 *
 * Usando:
 * import intercalar
 * intercalar.intercalar('AABBCCDDEE', '1', 2)
 */

static PyObject *
intercalar_intercalar(PyObject *self, PyObject *args){
    PyObject* result;
    char *texto, c, *intercalado, *t, *i;
    int passo, pos, tam;

    if (!PyArg_ParseTuple(args, "sci", &texto, &c, &passo))
        return NULL;

    if (passo < 1){
        PyErr_SetString(PyExc_ValueError, "Passo precisa ser maior que zero!");
        return NULL;
    }

    tam = strlen(texto);
    tam = tam / passo * (passo + 1) + tam % passo + 1;
    intercalado = (char*)malloc(tam);
    t = texto;
    i = intercalado;
    pos = 0;
    for (pos = 0; *t; pos++) {
        *(i++) = *(t++);
        if ((pos + 1) % passo == 0)
            *(i++) = c;
    }
    *i = '\0';

    result = Py_BuildValue("s", intercalado);

    free(intercalado);

    return result;
}

static PyMethodDef intercalar_methods[] = {
    {"intercalar",  intercalar_intercalar, METH_VARARGS,
     "Intercala 1 caracter a cada passo.\n"
     "Uso: intercalar(texto, caracter, passo)\n"
     "Return: texto intercalado"},
    {NULL, NULL, 0, NULL} /* Sentinela */
};

PyMODINIT_FUNC
initintercalar(void)
{
    (void) Py_InitModule("intercalar", intercalar_methods);
}