Product.c

product.c

#include <Python.h>
#include <stdio.h>
#include <string.h>

typedef struct {
    PyObject_HEAD
    char* trans;
    int len_letters;
    char* letters;
    int repeat;
    int iters;
    int init;
    int* values;
} product_struct;

PyObject* product_iter(PyObject *self)
{
    Py_INCREF(self);
    return self;
}

PyObject* product_iternext(PyObject *self)
{
    product_struct *p = (product_struct *)self;
    if (p->init < p->iters) {
        int i;
        for (i=p->repeat-1; i>=0; i--){
                if (p->values[i] == p->len_letters-1){
                        p->values[i] = 0;
                        p->trans[i] = p->letters[0];
                }else{
                        p->values[i]++;
                        p->trans[i] = p->letters[p->values[i]];
                        break;
                }
        }
        PyObject *tmp = Py_BuildValue("s", p->trans);
        p->init++;
        return tmp;
    } else {
        /* Raising of standard StopIteration exception with empty value. */
        PyErr_SetNone(PyExc_StopIteration);
        return NULL;
    }
}

static PyTypeObject productType = {
    PyObject_HEAD_INIT(NULL)
    0,                         /*ob_size*/
    "product",                 /*tp_name*/
    sizeof(product_struct),    /*tp_basicsize*/
    0,                         /*tp_itemsize*/
    0,                         /*tp_dealloc*/
    0,                         /*tp_print*/
    0,                         /*tp_getattr*/
    0,                         /*tp_setattr*/
    0,                         /*tp_compare*/
    0,                         /*tp_repr*/
    0,                         /*tp_as_number*/
    0,                         /*tp_as_sequence*/
    0,                         /*tp_as_mapping*/
    0,                         /*tp_hash */
    0,                         /*tp_call*/
    0,                         /*tp_str*/
    0,                         /*tp_getattro*/
    0,                         /*tp_setattro*/
    0,                         /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_ITER,
        /* tp_flags: Py_TPFLAGS_HAVE_ITER tells python to
             use tp_iter and tp_iternext fields. */
    "Internal product iterator object.",           /* tp_doc */
    0,  /* tp_traverse */
    0,  /* tp_clear */
    0,  /* tp_richcompare */
    0,  /* tp_weaklistoffset */
    product_iter,  /* tp_iter: __iter__() method */
    product_iternext  /* tp_iternext: next() method */
};

long pow(int a, int b)
{
    if (b<=0)
        return 1;
    else
        return a*pow(a,b-1);
}
void calculate(int *values, int number, int repeat, int len_letters)
{
    int i = 0;
    int accumulated = 0;

    for(i=repeat-1; i>=0; i--){
        values[i] = (number - accumulated) / pow(len_letters, i);
        accumulated = accumulated + values[i]*pow(len_letters, i);
    }
    values[repeat-1]--;
}

static PyObject* product(PyObject* self, PyObject *args)
{
    int repeat;
    int init;
    int iters;
    char* letters;
    product_struct *p;

    if (!PyArg_ParseTuple(args, "siii", &letters, &repeat, &init, &iters)) {
        return NULL;
    }
    //printf("%s %d %d %d", letters, repeat, init, iters);
    /* I don't need python callable __init__() method for this iterator,
         so I'll simply allocate it as PyObject and initialize it by hand. */

    p = PyObject_New(product_struct, &productType);
    if (!p) return NULL;


    int values[repeat];
    int len_letters = strlen(letters);
    calculate(values, init, repeat, len_letters);

    int i;
    p->values = malloc(repeat * sizeof(int));
    p->trans = malloc(repeat * sizeof(char));
    p->letters = malloc(repeat * sizeof(char));
    for (i=0; i < len_letters; i++){
        p->letters[i] = letters[i];
    }
    for (i=0; i < repeat; i++){
        p->values[i] = values[i];
        p->trans[i] = letters[values[i]];
    }
    p->len_letters = len_letters;
    p->repeat = repeat;
    p->iters = iters;
    p->init = init;
    return (PyObject *)p;
}

static PyMethodDef SpamMethods[] = {
    {"product",  product, METH_VARARGS, "the best help."},
    {NULL, NULL, 0, NULL}        /* Sentinel */
};

PyMODINIT_FUNC
initproduct(void)
{
    PyObject* m;

    productType.tp_new = PyType_GenericNew;
    if (PyType_Ready(&productType) < 0)  return;

    m = Py_InitModule("product", SpamMethods);

    Py_INCREF(&productType);
    PyModule_AddObject(m, "_product", (PyObject *)&productType);
}