cpython/Modules/itertoolsmodule.c

#include "Python.h"
#include "structmember.h"

/* Itertools module written and maintained
   by Raymond D. Hettinger <python@rcn.com>
   Copyright (c) 2003 Python Software Foundation.
   All rights reserved.
*/


/* groupby object ***********************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *it;
    PyObject *keyfunc;
    PyObject *tgtkey;
    PyObject *currkey;
    PyObject *currvalue;
} groupbyobject;

static PyTypeObject groupby_type;
static PyObject *_grouper_create(groupbyobject *, PyObject *);

static PyObject *
groupby_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    static char *kwargs[] = {"iterable", "key", NULL};
    groupbyobject *gbo;
    PyObject *it, *keyfunc = Py_None;

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:groupby", kwargs,
                                     &it, &keyfunc))
        return NULL;

    gbo = (groupbyobject *)type->tp_alloc(type, 0);
    if (gbo == NULL)
        return NULL;
    gbo->tgtkey = NULL;
    gbo->currkey = NULL;
    gbo->currvalue = NULL;
    gbo->keyfunc = keyfunc;
    Py_INCREF(keyfunc);
    gbo->it = PyObject_GetIter(it);
    if (gbo->it == NULL) {
        Py_DECREF(gbo);
        return NULL;
    }
    return (PyObject *)gbo;
}

static void
groupby_dealloc(groupbyobject *gbo)
{
    PyObject_GC_UnTrack(gbo);
    Py_XDECREF(gbo->it);
    Py_XDECREF(gbo->keyfunc);
    Py_XDECREF(gbo->tgtkey);
    Py_XDECREF(gbo->currkey);
    Py_XDECREF(gbo->currvalue);
    Py_TYPE(gbo)->tp_free(gbo);
}

static int
groupby_traverse(groupbyobject *gbo, visitproc visit, void *arg)
{
    Py_VISIT(gbo->it);
    Py_VISIT(gbo->keyfunc);
    Py_VISIT(gbo->tgtkey);
    Py_VISIT(gbo->currkey);
    Py_VISIT(gbo->currvalue);
    return 0;
}

static PyObject *
groupby_next(groupbyobject *gbo)
{
    PyObject *newvalue, *newkey, *r, *grouper, *tmp;

    /* skip to next iteration group */
    for (;;) {
        if (gbo->currkey == NULL)
            /* pass */;
        else if (gbo->tgtkey == NULL)
            break;
        else {
            int rcmp;

            rcmp = PyObject_RichCompareBool(gbo->tgtkey,
                                            gbo->currkey, Py_EQ);
            if (rcmp == -1)
                return NULL;
            else if (rcmp == 0)
                break;
        }

        newvalue = PyIter_Next(gbo->it);
        if (newvalue == NULL)
            return NULL;

        if (gbo->keyfunc == Py_None) {
            newkey = newvalue;
            Py_INCREF(newvalue);
        } else {
            newkey = PyObject_CallFunctionObjArgs(gbo->keyfunc,
                                                  newvalue, NULL);
            if (newkey == NULL) {
                Py_DECREF(newvalue);
                return NULL;
            }
        }

        tmp = gbo->currkey;
        gbo->currkey = newkey;
        Py_XDECREF(tmp);

        tmp = gbo->currvalue;
        gbo->currvalue = newvalue;
        Py_XDECREF(tmp);
    }

    Py_INCREF(gbo->currkey);
    tmp = gbo->tgtkey;
    gbo->tgtkey = gbo->currkey;
    Py_XDECREF(tmp);

    grouper = _grouper_create(gbo, gbo->tgtkey);
    if (grouper == NULL)
        return NULL;

    r = PyTuple_Pack(2, gbo->currkey, grouper);
    Py_DECREF(grouper);
    return r;
}

PyDoc_STRVAR(groupby_doc,
"groupby(iterable[, keyfunc]) -> create an iterator which returns\n\
(key, sub-iterator) grouped by each value of key(value).\n");

static PyTypeObject groupby_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.groupby",                /* tp_name */
    sizeof(groupbyobject),              /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)groupby_dealloc,        /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    groupby_doc,                        /* tp_doc */
    (traverseproc)groupby_traverse,     /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)groupby_next,         /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    groupby_new,                        /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* _grouper object (internal) ************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *parent;
    PyObject *tgtkey;
} _grouperobject;

static PyTypeObject _grouper_type;

static PyObject *
_grouper_create(groupbyobject *parent, PyObject *tgtkey)
{
    _grouperobject *igo;

    igo = PyObject_GC_New(_grouperobject, &_grouper_type);
    if (igo == NULL)
        return NULL;
    igo->parent = (PyObject *)parent;
    Py_INCREF(parent);
    igo->tgtkey = tgtkey;
    Py_INCREF(tgtkey);

    PyObject_GC_Track(igo);
    return (PyObject *)igo;
}

static void
_grouper_dealloc(_grouperobject *igo)
{
    PyObject_GC_UnTrack(igo);
    Py_DECREF(igo->parent);
    Py_DECREF(igo->tgtkey);
    PyObject_GC_Del(igo);
}

static int
_grouper_traverse(_grouperobject *igo, visitproc visit, void *arg)
{
    Py_VISIT(igo->parent);
    Py_VISIT(igo->tgtkey);
    return 0;
}

static PyObject *
_grouper_next(_grouperobject *igo)
{
    groupbyobject *gbo = (groupbyobject *)igo->parent;
    PyObject *newvalue, *newkey, *r;
    int rcmp;

    if (gbo->currvalue == NULL) {
        newvalue = PyIter_Next(gbo->it);
        if (newvalue == NULL)
            return NULL;

        if (gbo->keyfunc == Py_None) {
            newkey = newvalue;
            Py_INCREF(newvalue);
        } else {
            newkey = PyObject_CallFunctionObjArgs(gbo->keyfunc,
                                                  newvalue, NULL);
            if (newkey == NULL) {
                Py_DECREF(newvalue);
                return NULL;
            }
        }

        assert(gbo->currkey == NULL);
        gbo->currkey = newkey;
        gbo->currvalue = newvalue;
    }

    assert(gbo->currkey != NULL);
    rcmp = PyObject_RichCompareBool(igo->tgtkey, gbo->currkey, Py_EQ);
    if (rcmp <= 0)
        /* got any error or current group is end */
        return NULL;

    r = gbo->currvalue;
    gbo->currvalue = NULL;
    Py_CLEAR(gbo->currkey);

    return r;
}

static PyTypeObject _grouper_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools._grouper",               /* tp_name */
    sizeof(_grouperobject),             /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)_grouper_dealloc,       /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,            /* tp_flags */
    0,                                  /* tp_doc */
    (traverseproc)_grouper_traverse,/* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)_grouper_next,        /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    0,                                  /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};



/* tee object and with supporting function and objects ***************/

/* The teedataobject pre-allocates space for LINKCELLS number of objects.
   To help the object fit neatly inside cache lines (space for 16 to 32
   pointers), the value should be a multiple of 16 minus  space for
   the other structure members including PyHEAD overhead.  The larger the
   value, the less memory overhead per object and the less time spent
   allocating/deallocating new links.  The smaller the number, the less
   wasted space and the more rapid freeing of older data.
*/
#define LINKCELLS 57

typedef struct {
    PyObject_HEAD
    PyObject *it;
    int numread;
    PyObject *nextlink;
    PyObject *(values[LINKCELLS]);
} teedataobject;

typedef struct {
    PyObject_HEAD
    teedataobject *dataobj;
    int index;
    PyObject *weakreflist;
} teeobject;

static PyTypeObject teedataobject_type;

static PyObject *
teedataobject_new(PyObject *it)
{
    teedataobject *tdo;

    tdo = PyObject_GC_New(teedataobject, &teedataobject_type);
    if (tdo == NULL)
        return NULL;

    tdo->numread = 0;
    tdo->nextlink = NULL;
    Py_INCREF(it);
    tdo->it = it;
    PyObject_GC_Track(tdo);
    return (PyObject *)tdo;
}

static PyObject *
teedataobject_jumplink(teedataobject *tdo)
{
    if (tdo->nextlink == NULL)
        tdo->nextlink = teedataobject_new(tdo->it);
    Py_XINCREF(tdo->nextlink);
    return tdo->nextlink;
}

static PyObject *
teedataobject_getitem(teedataobject *tdo, int i)
{
    PyObject *value;

    assert(i < LINKCELLS);
    if (i < tdo->numread)
        value = tdo->values[i];
    else {
        /* this is the lead iterator, so fetch more data */
        assert(i == tdo->numread);
        value = PyIter_Next(tdo->it);
        if (value == NULL)
            return NULL;
        tdo->numread++;
        tdo->values[i] = value;
    }
    Py_INCREF(value);
    return value;
}

static int
teedataobject_traverse(teedataobject *tdo, visitproc visit, void * arg)
{
    int i;
    Py_VISIT(tdo->it);
    for (i = 0; i < tdo->numread; i++)
        Py_VISIT(tdo->values[i]);
    Py_VISIT(tdo->nextlink);
    return 0;
}

static int
teedataobject_clear(teedataobject *tdo)
{
    int i;
    Py_CLEAR(tdo->it);
    for (i=0 ; i<tdo->numread ; i++)
        Py_CLEAR(tdo->values[i]);
    Py_CLEAR(tdo->nextlink);
    return 0;
}

static void
teedataobject_dealloc(teedataobject *tdo)
{
    PyObject_GC_UnTrack(tdo);
    teedataobject_clear(tdo);
    PyObject_GC_Del(tdo);
}

PyDoc_STRVAR(teedataobject_doc, "Data container common to multiple tee objects.");

static PyTypeObject teedataobject_type = {
    PyVarObject_HEAD_INIT(0, 0)         /* Must fill in type value later */
    "itertools.tee_dataobject",                 /* tp_name */
    sizeof(teedataobject),                      /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)teedataobject_dealloc,          /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    0,                                          /* tp_repr */
    0,                                          /* tp_as_number */
    0,                                          /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,            /* tp_flags */
    teedataobject_doc,                          /* tp_doc */
    (traverseproc)teedataobject_traverse,       /* tp_traverse */
    (inquiry)teedataobject_clear,               /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    0,                                          /* tp_iter */
    0,                                          /* tp_iternext */
    0,                                          /* tp_methods */
    0,                                          /* tp_members */
    0,                                          /* tp_getset */
    0,                                          /* tp_base */
    0,                                          /* tp_dict */
    0,                                          /* tp_descr_get */
    0,                                          /* tp_descr_set */
    0,                                          /* tp_dictoffset */
    0,                                          /* tp_init */
    0,                                          /* tp_alloc */
    0,                                          /* tp_new */
    PyObject_GC_Del,                            /* tp_free */
};


static PyTypeObject tee_type;

static PyObject *
tee_next(teeobject *to)
{
    PyObject *value, *link;

    if (to->index >= LINKCELLS) {
        link = teedataobject_jumplink(to->dataobj);
        Py_DECREF(to->dataobj);
        to->dataobj = (teedataobject *)link;
        to->index = 0;
    }
    value = teedataobject_getitem(to->dataobj, to->index);
    if (value == NULL)
        return NULL;
    to->index++;
    return value;
}

static int
tee_traverse(teeobject *to, visitproc visit, void *arg)
{
    Py_VISIT((PyObject *)to->dataobj);
    return 0;
}

static PyObject *
tee_copy(teeobject *to)
{
    teeobject *newto;

    newto = PyObject_GC_New(teeobject, &tee_type);
    if (newto == NULL)
        return NULL;
    Py_INCREF(to->dataobj);
    newto->dataobj = to->dataobj;
    newto->index = to->index;
    newto->weakreflist = NULL;
    PyObject_GC_Track(newto);
    return (PyObject *)newto;
}

PyDoc_STRVAR(teecopy_doc, "Returns an independent iterator.");

static PyObject *
tee_fromiterable(PyObject *iterable)
{
    teeobject *to;
    PyObject *it = NULL;

    it = PyObject_GetIter(iterable);
    if (it == NULL)
        return NULL;
    if (PyObject_TypeCheck(it, &tee_type)) {
        to = (teeobject *)tee_copy((teeobject *)it);
        goto done;
    }

    to = PyObject_GC_New(teeobject, &tee_type);
    if (to == NULL)
        goto done;
    to->dataobj = (teedataobject *)teedataobject_new(it);
    if (!to->dataobj) {
        PyObject_GC_Del(to);
        to = NULL;
        goto done;
    }

    to->index = 0;
    to->weakreflist = NULL;
    PyObject_GC_Track(to);
done:
    Py_XDECREF(it);
    return (PyObject *)to;
}

static PyObject *
tee_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
    PyObject *iterable;

    if (!PyArg_UnpackTuple(args, "tee", 1, 1, &iterable))
        return NULL;
    return tee_fromiterable(iterable);
}

static int
tee_clear(teeobject *to)
{
    if (to->weakreflist != NULL)
        PyObject_ClearWeakRefs((PyObject *) to);
    Py_CLEAR(to->dataobj);
    return 0;
}

static void
tee_dealloc(teeobject *to)
{
    PyObject_GC_UnTrack(to);
    tee_clear(to);
    PyObject_GC_Del(to);
}

PyDoc_STRVAR(teeobject_doc,
"Iterator wrapped to make it copyable");

static PyMethodDef tee_methods[] = {
    {"__copy__",        (PyCFunction)tee_copy,  METH_NOARGS, teecopy_doc},
    {NULL,              NULL}           /* sentinel */
};

static PyTypeObject tee_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.tee",                    /* tp_name */
    sizeof(teeobject),                  /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)tee_dealloc,            /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    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_GC,            /* tp_flags */
    teeobject_doc,                      /* tp_doc */
    (traverseproc)tee_traverse,         /* tp_traverse */
    (inquiry)tee_clear,                 /* tp_clear */
    0,                                  /* tp_richcompare */
    offsetof(teeobject, weakreflist),           /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)tee_next,             /* tp_iternext */
    tee_methods,                        /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    tee_new,                            /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};

static PyObject *
tee(PyObject *self, PyObject *args)
{
    Py_ssize_t i, n=2;
    PyObject *it, *iterable, *copyable, *result;

    if (!PyArg_ParseTuple(args, "O|n", &iterable, &n))
        return NULL;
    if (n < 0) {
        PyErr_SetString(PyExc_ValueError, "n must be >= 0");
        return NULL;
    }
    result = PyTuple_New(n);
    if (result == NULL)
        return NULL;
    if (n == 0)
        return result;
    it = PyObject_GetIter(iterable);
    if (it == NULL) {
        Py_DECREF(result);
        return NULL;
    }
    if (!PyObject_HasAttrString(it, "__copy__")) {
        copyable = tee_fromiterable(it);
        Py_DECREF(it);
        if (copyable == NULL) {
            Py_DECREF(result);
            return NULL;
        }
    } else
        copyable = it;
    PyTuple_SET_ITEM(result, 0, copyable);
    for (i=1 ; i<n ; i++) {
        copyable = PyObject_CallMethod(copyable, "__copy__", NULL);
        if (copyable == NULL) {
            Py_DECREF(result);
            return NULL;
        }
        PyTuple_SET_ITEM(result, i, copyable);
    }
    return result;
}

PyDoc_STRVAR(tee_doc,
"tee(iterable, n=2) --> tuple of n independent iterators.");


/* cycle object **********************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *it;
    PyObject *saved;
    int firstpass;
} cycleobject;

static PyTypeObject cycle_type;

static PyObject *
cycle_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *it;
    PyObject *iterable;
    PyObject *saved;
    cycleobject *lz;

    if (type == &cycle_type && !_PyArg_NoKeywords("cycle()", kwds))
        return NULL;

    if (!PyArg_UnpackTuple(args, "cycle", 1, 1, &iterable))
        return NULL;

    /* Get iterator. */
    it = PyObject_GetIter(iterable);
    if (it == NULL)
        return NULL;

    saved = PyList_New(0);
    if (saved == NULL) {
        Py_DECREF(it);
        return NULL;
    }

    /* create cycleobject structure */
    lz = (cycleobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(it);
        Py_DECREF(saved);
        return NULL;
    }
    lz->it = it;
    lz->saved = saved;
    lz->firstpass = 0;

    return (PyObject *)lz;
}

static void
cycle_dealloc(cycleobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->saved);
    Py_XDECREF(lz->it);
    Py_TYPE(lz)->tp_free(lz);
}

static int
cycle_traverse(cycleobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->it);
    Py_VISIT(lz->saved);
    return 0;
}

static PyObject *
cycle_next(cycleobject *lz)
{
    PyObject *item;
    PyObject *it;
    PyObject *tmp;

    while (1) {
        item = PyIter_Next(lz->it);
        if (item != NULL) {
            if (!lz->firstpass && PyList_Append(lz->saved, item)) {
                Py_DECREF(item);
                return NULL;
            }
            return item;
        }
        if (PyErr_Occurred()) {
            if (PyErr_ExceptionMatches(PyExc_StopIteration))
                PyErr_Clear();
            else
                return NULL;
        }
        if (PyList_Size(lz->saved) == 0)
            return NULL;
        it = PyObject_GetIter(lz->saved);
        if (it == NULL)
            return NULL;
        tmp = lz->it;
        lz->it = it;
        lz->firstpass = 1;
        Py_DECREF(tmp);
    }
}

PyDoc_STRVAR(cycle_doc,
"cycle(iterable) --> cycle object\n\
\n\
Return elements from the iterable until it is exhausted.\n\
Then repeat the sequence indefinitely.");

static PyTypeObject cycle_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.cycle",                  /* tp_name */
    sizeof(cycleobject),                /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)cycle_dealloc,          /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    cycle_doc,                          /* tp_doc */
    (traverseproc)cycle_traverse,       /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)cycle_next,           /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    cycle_new,                          /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* dropwhile object **********************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *func;
    PyObject *it;
    long         start;
} dropwhileobject;

static PyTypeObject dropwhile_type;

static PyObject *
dropwhile_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *func, *seq;
    PyObject *it;
    dropwhileobject *lz;

    if (type == &dropwhile_type && !_PyArg_NoKeywords("dropwhile()", kwds))
        return NULL;

    if (!PyArg_UnpackTuple(args, "dropwhile", 2, 2, &func, &seq))
        return NULL;

    /* Get iterator. */
    it = PyObject_GetIter(seq);
    if (it == NULL)
        return NULL;

    /* create dropwhileobject structure */
    lz = (dropwhileobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(it);
        return NULL;
    }
    Py_INCREF(func);
    lz->func = func;
    lz->it = it;
    lz->start = 0;

    return (PyObject *)lz;
}

static void
dropwhile_dealloc(dropwhileobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->func);
    Py_XDECREF(lz->it);
    Py_TYPE(lz)->tp_free(lz);
}

static int
dropwhile_traverse(dropwhileobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->it);
    Py_VISIT(lz->func);
    return 0;
}

static PyObject *
dropwhile_next(dropwhileobject *lz)
{
    PyObject *item, *good;
    PyObject *it = lz->it;
    long ok;
    PyObject *(*iternext)(PyObject *);

    iternext = *Py_TYPE(it)->tp_iternext;
    for (;;) {
        item = iternext(it);
        if (item == NULL)
            return NULL;
        if (lz->start == 1)
            return item;

        good = PyObject_CallFunctionObjArgs(lz->func, item, NULL);
        if (good == NULL) {
            Py_DECREF(item);
            return NULL;
        }
        ok = PyObject_IsTrue(good);
        Py_DECREF(good);
        if (!ok) {
            lz->start = 1;
            return item;
        }
        Py_DECREF(item);
    }
}

PyDoc_STRVAR(dropwhile_doc,
"dropwhile(predicate, iterable) --> dropwhile object\n\
\n\
Drop items from the iterable while predicate(item) is true.\n\
Afterwards, return every element until the iterable is exhausted.");

static PyTypeObject dropwhile_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.dropwhile",              /* tp_name */
    sizeof(dropwhileobject),            /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)dropwhile_dealloc,      /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    dropwhile_doc,                      /* tp_doc */
    (traverseproc)dropwhile_traverse,    /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)dropwhile_next,       /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    dropwhile_new,                      /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* takewhile object **********************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *func;
    PyObject *it;
    long         stop;
} takewhileobject;

static PyTypeObject takewhile_type;

static PyObject *
takewhile_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *func, *seq;
    PyObject *it;
    takewhileobject *lz;

    if (type == &takewhile_type && !_PyArg_NoKeywords("takewhile()", kwds))
        return NULL;

    if (!PyArg_UnpackTuple(args, "takewhile", 2, 2, &func, &seq))
        return NULL;

    /* Get iterator. */
    it = PyObject_GetIter(seq);
    if (it == NULL)
        return NULL;

    /* create takewhileobject structure */
    lz = (takewhileobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(it);
        return NULL;
    }
    Py_INCREF(func);
    lz->func = func;
    lz->it = it;
    lz->stop = 0;

    return (PyObject *)lz;
}

static void
takewhile_dealloc(takewhileobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->func);
    Py_XDECREF(lz->it);
    Py_TYPE(lz)->tp_free(lz);
}

static int
takewhile_traverse(takewhileobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->it);
    Py_VISIT(lz->func);
    return 0;
}

static PyObject *
takewhile_next(takewhileobject *lz)
{
    PyObject *item, *good;
    PyObject *it = lz->it;
    long ok;

    if (lz->stop == 1)
        return NULL;

    item = (*Py_TYPE(it)->tp_iternext)(it);
    if (item == NULL)
        return NULL;

    good = PyObject_CallFunctionObjArgs(lz->func, item, NULL);
    if (good == NULL) {
        Py_DECREF(item);
        return NULL;
    }
    ok = PyObject_IsTrue(good);
    Py_DECREF(good);
    if (ok)
        return item;
    Py_DECREF(item);
    lz->stop = 1;
    return NULL;
}

PyDoc_STRVAR(takewhile_doc,
"takewhile(predicate, iterable) --> takewhile object\n\
\n\
Return successive entries from an iterable as long as the \n\
predicate evaluates to true for each entry.");

static PyTypeObject takewhile_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.takewhile",              /* tp_name */
    sizeof(takewhileobject),            /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)takewhile_dealloc,      /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    takewhile_doc,                      /* tp_doc */
    (traverseproc)takewhile_traverse,    /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)takewhile_next,       /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    takewhile_new,                      /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* islice object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *it;
    Py_ssize_t next;
    Py_ssize_t stop;
    Py_ssize_t step;
    Py_ssize_t cnt;
} isliceobject;

static PyTypeObject islice_type;

static PyObject *
islice_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *seq;
    Py_ssize_t start=0, stop=-1, step=1;
    PyObject *it, *a1=NULL, *a2=NULL, *a3=NULL;
    Py_ssize_t numargs;
    isliceobject *lz;

    if (type == &islice_type && !_PyArg_NoKeywords("islice()", kwds))
        return NULL;

    if (!PyArg_UnpackTuple(args, "islice", 2, 4, &seq, &a1, &a2, &a3))
        return NULL;

    numargs = PyTuple_Size(args);
    if (numargs == 2) {
        if (a1 != Py_None) {
            stop = PyLong_AsSsize_t(a1);
            if (stop == -1) {
                if (PyErr_Occurred())
                    PyErr_Clear();
                PyErr_SetString(PyExc_ValueError,
                   "Stop argument for islice() must be None or an integer: 0 <= x <= sys.maxsize.");
                return NULL;
            }
        }
    } else {
        if (a1 != Py_None)
            start = PyLong_AsSsize_t(a1);
        if (start == -1 && PyErr_Occurred())
            PyErr_Clear();
        if (a2 != Py_None) {
            stop = PyLong_AsSsize_t(a2);
            if (stop == -1) {
                if (PyErr_Occurred())
                    PyErr_Clear();
                PyErr_SetString(PyExc_ValueError,
                   "Stop argument for islice() must be None or an integer: 0 <= x <= sys.maxsize.");
                return NULL;
            }
        }
    }
    if (start<0 || stop<-1) {
        PyErr_SetString(PyExc_ValueError,
           "Indices for islice() must be None or an integer: 0 <= x <= sys.maxsize.");
        return NULL;
    }

    if (a3 != NULL) {
        if (a3 != Py_None)
            step = PyLong_AsSsize_t(a3);
        if (step == -1 && PyErr_Occurred())
            PyErr_Clear();
    }
    if (step<1) {
        PyErr_SetString(PyExc_ValueError,
           "Step for islice() must be a positive integer or None.");
        return NULL;
    }

    /* Get iterator. */
    it = PyObject_GetIter(seq);
    if (it == NULL)
        return NULL;

    /* create isliceobject structure */
    lz = (isliceobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(it);
        return NULL;
    }
    lz->it = it;
    lz->next = start;
    lz->stop = stop;
    lz->step = step;
    lz->cnt = 0L;

    return (PyObject *)lz;
}

static void
islice_dealloc(isliceobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->it);
    Py_TYPE(lz)->tp_free(lz);
}

static int
islice_traverse(isliceobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->it);
    return 0;
}

static PyObject *
islice_next(isliceobject *lz)
{
    PyObject *item;
    PyObject *it = lz->it;
    Py_ssize_t stop = lz->stop;
    Py_ssize_t oldnext;
    PyObject *(*iternext)(PyObject *);

    iternext = *Py_TYPE(it)->tp_iternext;
    while (lz->cnt < lz->next) {
        item = iternext(it);
        if (item == NULL)
            return NULL;
        Py_DECREF(item);
        lz->cnt++;
    }
    if (stop != -1 && lz->cnt >= stop)
        return NULL;
    item = iternext(it);
    if (item == NULL)
        return NULL;
    lz->cnt++;
    oldnext = lz->next;
    lz->next += lz->step;
    if (lz->next < oldnext || (stop != -1 && lz->next > stop))
        lz->next = stop;
    return item;
}

PyDoc_STRVAR(islice_doc,
"islice(iterable, [start,] stop [, step]) --> islice object\n\
\n\
Return an iterator whose next() method returns selected values from an\n\
iterable.  If start is specified, will skip all preceding elements;\n\
otherwise, start defaults to zero.  Step defaults to one.  If\n\
specified as another value, step determines how many values are \n\
skipped between successive calls.  Works like a slice() on a list\n\
but returns an iterator.");

static PyTypeObject islice_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.islice",                 /* tp_name */
    sizeof(isliceobject),               /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)islice_dealloc,         /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    islice_doc,                         /* tp_doc */
    (traverseproc)islice_traverse,      /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)islice_next,          /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    islice_new,                         /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* starmap object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *func;
    PyObject *it;
} starmapobject;

static PyTypeObject starmap_type;

static PyObject *
starmap_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *func, *seq;
    PyObject *it;
    starmapobject *lz;

    if (type == &starmap_type && !_PyArg_NoKeywords("starmap()", kwds))
        return NULL;

    if (!PyArg_UnpackTuple(args, "starmap", 2, 2, &func, &seq))
        return NULL;

    /* Get iterator. */
    it = PyObject_GetIter(seq);
    if (it == NULL)
        return NULL;

    /* create starmapobject structure */
    lz = (starmapobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(it);
        return NULL;
    }
    Py_INCREF(func);
    lz->func = func;
    lz->it = it;

    return (PyObject *)lz;
}

static void
starmap_dealloc(starmapobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->func);
    Py_XDECREF(lz->it);
    Py_TYPE(lz)->tp_free(lz);
}

static int
starmap_traverse(starmapobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->it);
    Py_VISIT(lz->func);
    return 0;
}

static PyObject *
starmap_next(starmapobject *lz)
{
    PyObject *args;
    PyObject *result;
    PyObject *it = lz->it;

    args = (*Py_TYPE(it)->tp_iternext)(it);
    if (args == NULL)
        return NULL;
    if (!PyTuple_CheckExact(args)) {
        PyObject *newargs = PySequence_Tuple(args);
        Py_DECREF(args);
        if (newargs == NULL)
            return NULL;
        args = newargs;
    }
    result = PyObject_Call(lz->func, args, NULL);
    Py_DECREF(args);
    return result;
}

PyDoc_STRVAR(starmap_doc,
"starmap(function, sequence) --> starmap object\n\
\n\
Return an iterator whose values are returned from the function evaluated\n\
with a argument tuple taken from the given sequence.");

static PyTypeObject starmap_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.starmap",                /* tp_name */
    sizeof(starmapobject),              /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)starmap_dealloc,        /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    starmap_doc,                        /* tp_doc */
    (traverseproc)starmap_traverse,     /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)starmap_next,         /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    starmap_new,                        /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* chain object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *source;                   /* Iterator over input iterables */
    PyObject *active;                   /* Currently running input iterator */
} chainobject;

static PyTypeObject chain_type;

static PyObject *
chain_new_internal(PyTypeObject *type, PyObject *source)
{
    chainobject *lz;

    lz = (chainobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(source);
        return NULL;
    }

    lz->source = source;
    lz->active = NULL;
    return (PyObject *)lz;
}

static PyObject *
chain_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *source;

    if (type == &chain_type && !_PyArg_NoKeywords("chain()", kwds))
        return NULL;

    source = PyObject_GetIter(args);
    if (source == NULL)
        return NULL;

    return chain_new_internal(type, source);
}

static PyObject *
chain_new_from_iterable(PyTypeObject *type, PyObject *arg)
{
    PyObject *source;

    source = PyObject_GetIter(arg);
    if (source == NULL)
        return NULL;

    return chain_new_internal(type, source);
}

static void
chain_dealloc(chainobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->active);
    Py_XDECREF(lz->source);
    Py_TYPE(lz)->tp_free(lz);
}

static int
chain_traverse(chainobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->source);
    Py_VISIT(lz->active);
    return 0;
}

static PyObject *
chain_next(chainobject *lz)
{
    PyObject *item;

    if (lz->source == NULL)
        return NULL;                                    /* already stopped */

    if (lz->active == NULL) {
        PyObject *iterable = PyIter_Next(lz->source);
        if (iterable == NULL) {
            Py_CLEAR(lz->source);
            return NULL;                                /* no more input sources */
        }
        lz->active = PyObject_GetIter(iterable);
        Py_DECREF(iterable);
        if (lz->active == NULL) {
            Py_CLEAR(lz->source);
            return NULL;                                /* input not iterable */
        }
    }
    item = PyIter_Next(lz->active);
    if (item != NULL)
        return item;
    if (PyErr_Occurred()) {
        if (PyErr_ExceptionMatches(PyExc_StopIteration))
            PyErr_Clear();
        else
            return NULL;                                /* input raised an exception */
    }
    Py_CLEAR(lz->active);
    return chain_next(lz);                      /* recurse and use next active */
}

PyDoc_STRVAR(chain_doc,
"chain(*iterables) --> chain object\n\
\n\
Return a chain object whose .__next__() method returns elements from the\n\
first iterable until it is exhausted, then elements from the next\n\
iterable, until all of the iterables are exhausted.");

PyDoc_STRVAR(chain_from_iterable_doc,
"chain.from_iterable(iterable) --> chain object\n\
\n\
Alternate chain() contructor taking a single iterable argument\n\
that evaluates lazily.");

static PyMethodDef chain_methods[] = {
    {"from_iterable", (PyCFunction) chain_new_from_iterable,            METH_O | METH_CLASS,
        chain_from_iterable_doc},
    {NULL,              NULL}   /* sentinel */
};

static PyTypeObject chain_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.chain",                  /* tp_name */
    sizeof(chainobject),                /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)chain_dealloc,          /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    chain_doc,                          /* tp_doc */
    (traverseproc)chain_traverse,       /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)chain_next,           /* tp_iternext */
    chain_methods,                      /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    chain_new,                          /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* product object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *pools;                    /* tuple of pool tuples */
    Py_ssize_t *indices;            /* one index per pool */
    PyObject *result;               /* most recently returned result tuple */
    int stopped;                    /* set to 1 when the product iterator is exhausted */
} productobject;

static PyTypeObject product_type;

static PyObject *
product_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    productobject *lz;
    Py_ssize_t nargs, npools, repeat=1;
    PyObject *pools = NULL;
    Py_ssize_t *indices = NULL;
    Py_ssize_t i;

    if (kwds != NULL) {
        char *kwlist[] = {"repeat", 0};
        PyObject *tmpargs = PyTuple_New(0);
        if (tmpargs == NULL)
            return NULL;
        if (!PyArg_ParseTupleAndKeywords(tmpargs, kwds, "|n:product", kwlist, &repeat)) {
            Py_DECREF(tmpargs);
            return NULL;
        }
        Py_DECREF(tmpargs);
        if (repeat < 0) {
            PyErr_SetString(PyExc_ValueError,
                            "repeat argument cannot be negative");
            return NULL;
        }
    }

    assert(PyTuple_Check(args));
    nargs = (repeat == 0) ? 0 : PyTuple_GET_SIZE(args);
    npools = nargs * repeat;

    indices = PyMem_Malloc(npools * sizeof(Py_ssize_t));
    if (indices == NULL) {
        PyErr_NoMemory();
        goto error;
    }

    pools = PyTuple_New(npools);
    if (pools == NULL)
        goto error;

    for (i=0; i < nargs ; ++i) {
        PyObject *item = PyTuple_GET_ITEM(args, i);
        PyObject *pool = PySequence_Tuple(item);
        if (pool == NULL)
            goto error;
        PyTuple_SET_ITEM(pools, i, pool);
        indices[i] = 0;
    }
    for ( ; i < npools; ++i) {
        PyObject *pool = PyTuple_GET_ITEM(pools, i - nargs);
        Py_INCREF(pool);
        PyTuple_SET_ITEM(pools, i, pool);
        indices[i] = 0;
    }

    /* create productobject structure */
    lz = (productobject *)type->tp_alloc(type, 0);
    if (lz == NULL)
        goto error;

    lz->pools = pools;
    lz->indices = indices;
    lz->result = NULL;
    lz->stopped = 0;

    return (PyObject *)lz;

error:
    if (indices != NULL)
        PyMem_Free(indices);
    Py_XDECREF(pools);
    return NULL;
}

static void
product_dealloc(productobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->pools);
    Py_XDECREF(lz->result);
    if (lz->indices != NULL)
        PyMem_Free(lz->indices);
    Py_TYPE(lz)->tp_free(lz);
}

static int
product_traverse(productobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->pools);
    Py_VISIT(lz->result);
    return 0;
}

static PyObject *
product_next(productobject *lz)
{
    PyObject *pool;
    PyObject *elem;
    PyObject *oldelem;
    PyObject *pools = lz->pools;
    PyObject *result = lz->result;
    Py_ssize_t npools = PyTuple_GET_SIZE(pools);
    Py_ssize_t i;

    if (lz->stopped)
        return NULL;

    if (result == NULL) {
        /* On the first pass, return an initial tuple filled with the
           first element from each pool. */
        result = PyTuple_New(npools);
        if (result == NULL)
            goto empty;
        lz->result = result;
        for (i=0; i < npools; i++) {
            pool = PyTuple_GET_ITEM(pools, i);
            if (PyTuple_GET_SIZE(pool) == 0)
                goto empty;
            elem = PyTuple_GET_ITEM(pool, 0);
            Py_INCREF(elem);
            PyTuple_SET_ITEM(result, i, elem);
        }
    } else {
        Py_ssize_t *indices = lz->indices;

        /* Copy the previous result tuple or re-use it if available */
        if (Py_REFCNT(result) > 1) {
            PyObject *old_result = result;
            result = PyTuple_New(npools);
            if (result == NULL)
                goto empty;
            lz->result = result;
            for (i=0; i < npools; i++) {
                elem = PyTuple_GET_ITEM(old_result, i);
                Py_INCREF(elem);
                PyTuple_SET_ITEM(result, i, elem);
            }
            Py_DECREF(old_result);
        }
        /* Now, we've got the only copy so we can update it in-place */
        assert (npools==0 || Py_REFCNT(result) == 1);

        /* Update the pool indices right-to-left.  Only advance to the
           next pool when the previous one rolls-over */
        for (i=npools-1 ; i >= 0 ; i--) {
            pool = PyTuple_GET_ITEM(pools, i);
            indices[i]++;
            if (indices[i] == PyTuple_GET_SIZE(pool)) {
                /* Roll-over and advance to next pool */
                indices[i] = 0;
                elem = PyTuple_GET_ITEM(pool, 0);
                Py_INCREF(elem);
                oldelem = PyTuple_GET_ITEM(result, i);
                PyTuple_SET_ITEM(result, i, elem);
                Py_DECREF(oldelem);
            } else {
                /* No rollover. Just increment and stop here. */
                elem = PyTuple_GET_ITEM(pool, indices[i]);
                Py_INCREF(elem);
                oldelem = PyTuple_GET_ITEM(result, i);
                PyTuple_SET_ITEM(result, i, elem);
                Py_DECREF(oldelem);
                break;
            }
        }

        /* If i is negative, then the indices have all rolled-over
           and we're done. */
        if (i < 0)
            goto empty;
    }

    Py_INCREF(result);
    return result;

empty:
    lz->stopped = 1;
    return NULL;
}

PyDoc_STRVAR(product_doc,
"product(*iterables) --> product object\n\
\n\
Cartesian product of input iterables.  Equivalent to nested for-loops.\n\n\
For example, product(A, B) returns the same as:  ((x,y) for x in A for y in B).\n\
The leftmost iterators are in the outermost for-loop, so the output tuples\n\
cycle in a manner similar to an odometer (with the rightmost element changing\n\
on every iteration).\n\n\
To compute the product of an iterable with itself, specify the number\n\
of repetitions with the optional repeat keyword argument. For example,\n\
product(A, repeat=4) means the same as product(A, A, A, A).\n\n\
product('ab', range(3)) --> ('a',0) ('a',1) ('a',2) ('b',0) ('b',1) ('b',2)\n\
product((0,1), (0,1), (0,1)) --> (0,0,0) (0,0,1) (0,1,0) (0,1,1) (1,0,0) ...");

static PyTypeObject product_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.product",                /* tp_name */
    sizeof(productobject),      /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)product_dealloc,        /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    product_doc,                        /* tp_doc */
    (traverseproc)product_traverse,     /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)product_next,         /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    product_new,                        /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* combinations object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *pool;                     /* input converted to a tuple */
    Py_ssize_t *indices;            /* one index per result element */
    PyObject *result;               /* most recently returned result tuple */
    Py_ssize_t r;                       /* size of result tuple */
    int stopped;                        /* set to 1 when the combinations iterator is exhausted */
} combinationsobject;

static PyTypeObject combinations_type;

static PyObject *
combinations_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    combinationsobject *co;
    Py_ssize_t n;
    Py_ssize_t r;
    PyObject *pool = NULL;
    PyObject *iterable = NULL;
    Py_ssize_t *indices = NULL;
    Py_ssize_t i;
    static char *kwargs[] = {"iterable", "r", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "On:combinations", kwargs,
                                     &iterable, &r))
        return NULL;

    pool = PySequence_Tuple(iterable);
    if (pool == NULL)
        goto error;
    n = PyTuple_GET_SIZE(pool);
    if (r < 0) {
        PyErr_SetString(PyExc_ValueError, "r must be non-negative");
        goto error;
    }

    indices = PyMem_Malloc(r * sizeof(Py_ssize_t));
    if (indices == NULL) {
        PyErr_NoMemory();
        goto error;
    }

    for (i=0 ; i<r ; i++)
        indices[i] = i;

    /* create combinationsobject structure */
    co = (combinationsobject *)type->tp_alloc(type, 0);
    if (co == NULL)
        goto error;

    co->pool = pool;
    co->indices = indices;
    co->result = NULL;
    co->r = r;
    co->stopped = r > n ? 1 : 0;

    return (PyObject *)co;

error:
    if (indices != NULL)
        PyMem_Free(indices);
    Py_XDECREF(pool);
    return NULL;
}

static void
combinations_dealloc(combinationsobject *co)
{
    PyObject_GC_UnTrack(co);
    Py_XDECREF(co->pool);
    Py_XDECREF(co->result);
    if (co->indices != NULL)
        PyMem_Free(co->indices);
    Py_TYPE(co)->tp_free(co);
}

static int
combinations_traverse(combinationsobject *co, visitproc visit, void *arg)
{
    Py_VISIT(co->pool);
    Py_VISIT(co->result);
    return 0;
}

static PyObject *
combinations_next(combinationsobject *co)
{
    PyObject *elem;
    PyObject *oldelem;
    PyObject *pool = co->pool;
    Py_ssize_t *indices = co->indices;
    PyObject *result = co->result;
    Py_ssize_t n = PyTuple_GET_SIZE(pool);
    Py_ssize_t r = co->r;
    Py_ssize_t i, j, index;

    if (co->stopped)
        return NULL;

    if (result == NULL) {
        /* On the first pass, initialize result tuple using the indices */
        result = PyTuple_New(r);
        if (result == NULL)
            goto empty;
        co->result = result;
        for (i=0; i<r ; i++) {
            index = indices[i];
            elem = PyTuple_GET_ITEM(pool, index);
            Py_INCREF(elem);
            PyTuple_SET_ITEM(result, i, elem);
        }
    } else {
        /* Copy the previous result tuple or re-use it if available */
        if (Py_REFCNT(result) > 1) {
            PyObject *old_result = result;
            result = PyTuple_New(r);
            if (result == NULL)
                goto empty;
            co->result = result;
            for (i=0; i<r ; i++) {
                elem = PyTuple_GET_ITEM(old_result, i);
                Py_INCREF(elem);
                PyTuple_SET_ITEM(result, i, elem);
            }
            Py_DECREF(old_result);
        }
        /* Now, we've got the only copy so we can update it in-place
         * CPython's empty tuple is a singleton and cached in
         * PyTuple's freelist.
         */
        assert(r == 0 || Py_REFCNT(result) == 1);

        /* Scan indices right-to-left until finding one that is not
           at its maximum (i + n - r). */
        for (i=r-1 ; i >= 0 && indices[i] == i+n-r ; i--)
            ;

        /* If i is negative, then the indices are all at
           their maximum value and we're done. */
        if (i < 0)
            goto empty;

        /* Increment the current index which we know is not at its
           maximum.  Then move back to the right setting each index
           to its lowest possible value (one higher than the index
           to its left -- this maintains the sort order invariant). */
        indices[i]++;
        for (j=i+1 ; j<r ; j++)
            indices[j] = indices[j-1] + 1;

        /* Update the result tuple for the new indices
           starting with i, the leftmost index that changed */
        for ( ; i<r ; i++) {
            index = indices[i];
            elem = PyTuple_GET_ITEM(pool, index);
            Py_INCREF(elem);
            oldelem = PyTuple_GET_ITEM(result, i);
            PyTuple_SET_ITEM(result, i, elem);
            Py_DECREF(oldelem);
        }
    }

    Py_INCREF(result);
    return result;

empty:
    co->stopped = 1;
    return NULL;
}

PyDoc_STRVAR(combinations_doc,
"combinations(iterable, r) --> combinations object\n\
\n\
Return successive r-length combinations of elements in the iterable.\n\n\
combinations(range(4), 3) --> (0,1,2), (0,1,3), (0,2,3), (1,2,3)");

static PyTypeObject combinations_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.combinations",                   /* tp_name */
    sizeof(combinationsobject),         /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)combinations_dealloc,           /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    combinations_doc,                           /* tp_doc */
    (traverseproc)combinations_traverse,        /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)combinations_next,            /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    combinations_new,                           /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* combinations with replacement object *******************************************/

/* Equivalent to:

        def combinations_with_replacement(iterable, r):
            "combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC"
            # number items returned:  (n+r-1)! / r! / (n-1)!
            pool = tuple(iterable)
            n = len(pool)
            indices = [0] * r
            yield tuple(pool[i] for i in indices)
            while 1:
                for i in reversed(range(r)):
                    if indices[i] != n - 1:
                        break
                else:
                    return
                indices[i:] = [indices[i] + 1] * (r - i)
                yield tuple(pool[i] for i in indices)

        def combinations_with_replacement2(iterable, r):
            'Alternate version that filters from product()'
            pool = tuple(iterable)
            n = len(pool)
            for indices in product(range(n), repeat=r):
                if sorted(indices) == list(indices):
                    yield tuple(pool[i] for i in indices)
*/
typedef struct {
    PyObject_HEAD
    PyObject *pool;                     /* input converted to a tuple */
    Py_ssize_t *indices;    /* one index per result element */
    PyObject *result;       /* most recently returned result tuple */
    Py_ssize_t r;                       /* size of result tuple */
    int stopped;                        /* set to 1 when the cwr iterator is exhausted */
} cwrobject;

static PyTypeObject cwr_type;

static PyObject *
cwr_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    cwrobject *co;
    Py_ssize_t n;
    Py_ssize_t r;
    PyObject *pool = NULL;
    PyObject *iterable = NULL;
    Py_ssize_t *indices = NULL;
    Py_ssize_t i;
    static char *kwargs[] = {"iterable", "r", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "On:combinations_with_replacement", kwargs,
                                     &iterable, &r))
        return NULL;

    pool = PySequence_Tuple(iterable);
    if (pool == NULL)
        goto error;
    n = PyTuple_GET_SIZE(pool);
    if (r < 0) {
        PyErr_SetString(PyExc_ValueError, "r must be non-negative");
        goto error;
    }

    indices = PyMem_Malloc(r * sizeof(Py_ssize_t));
    if (indices == NULL) {
        PyErr_NoMemory();
        goto error;
    }

    for (i=0 ; i<r ; i++)
        indices[i] = 0;

    /* create cwrobject structure */
    co = (cwrobject *)type->tp_alloc(type, 0);
    if (co == NULL)
        goto error;

    co->pool = pool;
    co->indices = indices;
    co->result = NULL;
    co->r = r;
    co->stopped = !n && r;

    return (PyObject *)co;

error:
    if (indices != NULL)
        PyMem_Free(indices);
    Py_XDECREF(pool);
    return NULL;
}

static void
cwr_dealloc(cwrobject *co)
{
    PyObject_GC_UnTrack(co);
    Py_XDECREF(co->pool);
    Py_XDECREF(co->result);
    if (co->indices != NULL)
        PyMem_Free(co->indices);
    Py_TYPE(co)->tp_free(co);
}

static int
cwr_traverse(cwrobject *co, visitproc visit, void *arg)
{
    Py_VISIT(co->pool);
    Py_VISIT(co->result);
    return 0;
}

static PyObject *
cwr_next(cwrobject *co)
{
    PyObject *elem;
    PyObject *oldelem;
    PyObject *pool = co->pool;
    Py_ssize_t *indices = co->indices;
    PyObject *result = co->result;
    Py_ssize_t n = PyTuple_GET_SIZE(pool);
    Py_ssize_t r = co->r;
    Py_ssize_t i, j, index;

    if (co->stopped)
        return NULL;

    if (result == NULL) {
        /* On the first pass, initialize result tuple using the indices */
        result = PyTuple_New(r);
        if (result == NULL)
            goto empty;
        co->result = result;
        for (i=0; i<r ; i++) {
            index = indices[i];
            elem = PyTuple_GET_ITEM(pool, index);
            Py_INCREF(elem);
            PyTuple_SET_ITEM(result, i, elem);
        }
    } else {
        /* Copy the previous result tuple or re-use it if available */
        if (Py_REFCNT(result) > 1) {
            PyObject *old_result = result;
            result = PyTuple_New(r);
            if (result == NULL)
                goto empty;
            co->result = result;
            for (i=0; i<r ; i++) {
                elem = PyTuple_GET_ITEM(old_result, i);
                Py_INCREF(elem);
                PyTuple_SET_ITEM(result, i, elem);
            }
            Py_DECREF(old_result);
        }
        /* Now, we've got the only copy so we can update it in-place CPython's
           empty tuple is a singleton and cached in PyTuple's freelist. */
        assert(r == 0 || Py_REFCNT(result) == 1);

    /* Scan indices right-to-left until finding one that is not
     * at its maximum (n-1). */
        for (i=r-1 ; i >= 0 && indices[i] == n-1; i--)
            ;

        /* If i is negative, then the indices are all at
       their maximum value and we're done. */
        if (i < 0)
            goto empty;

        /* Increment the current index which we know is not at its
       maximum.  Then set all to the right to the same value. */
        indices[i]++;
        for (j=i+1 ; j<r ; j++)
            indices[j] = indices[j-1];

        /* Update the result tuple for the new indices
           starting with i, the leftmost index that changed */
        for ( ; i<r ; i++) {
            index = indices[i];
            elem = PyTuple_GET_ITEM(pool, index);
            Py_INCREF(elem);
            oldelem = PyTuple_GET_ITEM(result, i);
            PyTuple_SET_ITEM(result, i, elem);
            Py_DECREF(oldelem);
        }
    }

    Py_INCREF(result);
    return result;

empty:
    co->stopped = 1;
    return NULL;
}

PyDoc_STRVAR(cwr_doc,
"combinations_with_replacement(iterable, r) --> combinations_with_replacement object\n\
\n\
Return successive r-length combinations of elements in the iterable\n\
allowing individual elements to have successive repeats.\n\
combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC");

static PyTypeObject cwr_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.combinations_with_replacement",                  /* tp_name */
    sizeof(cwrobject),                  /* tp_basicsize */
    0,                                                  /* tp_itemsize */
    /* methods */
    (destructor)cwr_dealloc,            /* tp_dealloc */
    0,                                                  /* tp_print */
    0,                                                  /* tp_getattr */
    0,                                                  /* tp_setattr */
    0,                                                  /* tp_reserved */
    0,                                                  /* tp_repr */
    0,                                                  /* tp_as_number */
    0,                                                  /* tp_as_sequence */
    0,                                                  /* tp_as_mapping */
    0,                                                  /* tp_hash */
    0,                                                  /* tp_call */
    0,                                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                                  /* tp_setattro */
    0,                                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    cwr_doc,                                    /* tp_doc */
    (traverseproc)cwr_traverse,         /* tp_traverse */
    0,                                                  /* tp_clear */
    0,                                                  /* tp_richcompare */
    0,                                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)cwr_next,     /* tp_iternext */
    0,                                                  /* tp_methods */
    0,                                                  /* tp_members */
    0,                                                  /* tp_getset */
    0,                                                  /* tp_base */
    0,                                                  /* tp_dict */
    0,                                                  /* tp_descr_get */
    0,                                                  /* tp_descr_set */
    0,                                                  /* tp_dictoffset */
    0,                                                  /* tp_init */
    0,                                                  /* tp_alloc */
    cwr_new,                                    /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* permutations object ************************************************************

def permutations(iterable, r=None):
    'permutations(range(3), 2) --> (0,1) (0,2) (1,0) (1,2) (2,0) (2,1)'
    pool = tuple(iterable)
    n = len(pool)
    r = n if r is None else r
    indices = range(n)
    cycles = range(n-r+1, n+1)[::-1]
    yield tuple(pool[i] for i in indices[:r])
    while n:
    for i in reversed(range(r)):
        cycles[i] -= 1
        if cycles[i] == 0:
        indices[i:] = indices[i+1:] + indices[i:i+1]
        cycles[i] = n - i
        else:
        j = cycles[i]
        indices[i], indices[-j] = indices[-j], indices[i]
        yield tuple(pool[i] for i in indices[:r])
        break
    else:
        return
*/

typedef struct {
    PyObject_HEAD
    PyObject *pool;                     /* input converted to a tuple */
    Py_ssize_t *indices;            /* one index per element in the pool */
    Py_ssize_t *cycles;                 /* one rollover counter per element in the result */
    PyObject *result;               /* most recently returned result tuple */
    Py_ssize_t r;                       /* size of result tuple */
    int stopped;                        /* set to 1 when the permutations iterator is exhausted */
} permutationsobject;

static PyTypeObject permutations_type;

static PyObject *
permutations_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    permutationsobject *po;
    Py_ssize_t n;
    Py_ssize_t r;
    PyObject *robj = Py_None;
    PyObject *pool = NULL;
    PyObject *iterable = NULL;
    Py_ssize_t *indices = NULL;
    Py_ssize_t *cycles = NULL;
    Py_ssize_t i;
    static char *kwargs[] = {"iterable", "r", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:permutations", kwargs,
                                     &iterable, &robj))
        return NULL;

    pool = PySequence_Tuple(iterable);
    if (pool == NULL)
        goto error;
    n = PyTuple_GET_SIZE(pool);

    r = n;
    if (robj != Py_None) {
        if (!PyLong_Check(robj)) {
            PyErr_SetString(PyExc_TypeError, "Expected int as r");
            goto error;
        }
        r = PyLong_AsSsize_t(robj);
        if (r == -1 && PyErr_Occurred())
            goto error;
    }
    if (r < 0) {
        PyErr_SetString(PyExc_ValueError, "r must be non-negative");
        goto error;
    }

    indices = PyMem_Malloc(n * sizeof(Py_ssize_t));
    cycles = PyMem_Malloc(r * sizeof(Py_ssize_t));
    if (indices == NULL || cycles == NULL) {
        PyErr_NoMemory();
        goto error;
    }

    for (i=0 ; i<n ; i++)
        indices[i] = i;
    for (i=0 ; i<r ; i++)
        cycles[i] = n - i;

    /* create permutationsobject structure */
    po = (permutationsobject *)type->tp_alloc(type, 0);
    if (po == NULL)
        goto error;

    po->pool = pool;
    po->indices = indices;
    po->cycles = cycles;
    po->result = NULL;
    po->r = r;
    po->stopped = r > n ? 1 : 0;

    return (PyObject *)po;

error:
    if (indices != NULL)
        PyMem_Free(indices);
    if (cycles != NULL)
        PyMem_Free(cycles);
    Py_XDECREF(pool);
    return NULL;
}

static void
permutations_dealloc(permutationsobject *po)
{
    PyObject_GC_UnTrack(po);
    Py_XDECREF(po->pool);
    Py_XDECREF(po->result);
    PyMem_Free(po->indices);
    PyMem_Free(po->cycles);
    Py_TYPE(po)->tp_free(po);
}

static int
permutations_traverse(permutationsobject *po, visitproc visit, void *arg)
{
    Py_VISIT(po->pool);
    Py_VISIT(po->result);
    return 0;
}

static PyObject *
permutations_next(permutationsobject *po)
{
    PyObject *elem;
    PyObject *oldelem;
    PyObject *pool = po->pool;
    Py_ssize_t *indices = po->indices;
    Py_ssize_t *cycles = po->cycles;
    PyObject *result = po->result;
    Py_ssize_t n = PyTuple_GET_SIZE(pool);
    Py_ssize_t r = po->r;
    Py_ssize_t i, j, k, index;

    if (po->stopped)
        return NULL;

    if (result == NULL) {
        /* On the first pass, initialize result tuple using the indices */
        result = PyTuple_New(r);
        if (result == NULL)
            goto empty;
        po->result = result;
        for (i=0; i<r ; i++) {
            index = indices[i];
            elem = PyTuple_GET_ITEM(pool, index);
            Py_INCREF(elem);
            PyTuple_SET_ITEM(result, i, elem);
        }
    } else {
        if (n == 0)
            goto empty;

        /* Copy the previous result tuple or re-use it if available */
        if (Py_REFCNT(result) > 1) {
            PyObject *old_result = result;
            result = PyTuple_New(r);
            if (result == NULL)
                goto empty;
            po->result = result;
            for (i=0; i<r ; i++) {
                elem = PyTuple_GET_ITEM(old_result, i);
                Py_INCREF(elem);
                PyTuple_SET_ITEM(result, i, elem);
            }
            Py_DECREF(old_result);
        }
        /* Now, we've got the only copy so we can update it in-place */
        assert(r == 0 || Py_REFCNT(result) == 1);

        /* Decrement rightmost cycle, moving leftward upon zero rollover */
        for (i=r-1 ; i>=0 ; i--) {
            cycles[i] -= 1;
            if (cycles[i] == 0) {
                /* rotatation: indices[i:] = indices[i+1:] + indices[i:i+1] */
                index = indices[i];
                for (j=i ; j<n-1 ; j++)
                    indices[j] = indices[j+1];
                indices[n-1] = index;
                cycles[i] = n - i;
            } else {
                j = cycles[i];
                index = indices[i];
                indices[i] = indices[n-j];
                indices[n-j] = index;

                for (k=i; k<r ; k++) {
                    /* start with i, the leftmost element that changed */
                    /* yield tuple(pool[k] for k in indices[:r]) */
                    index = indices[k];
                    elem = PyTuple_GET_ITEM(pool, index);
                    Py_INCREF(elem);
                    oldelem = PyTuple_GET_ITEM(result, k);
                    PyTuple_SET_ITEM(result, k, elem);
                    Py_DECREF(oldelem);
                }
                break;
            }
        }
        /* If i is negative, then the cycles have all
           rolled-over and we're done. */
        if (i < 0)
            goto empty;
    }
    Py_INCREF(result);
    return result;

empty:
    po->stopped = 1;
    return NULL;
}

PyDoc_STRVAR(permutations_doc,
"permutations(iterable[, r]) --> permutations object\n\
\n\
Return successive r-length permutations of elements in the iterable.\n\n\
permutations(range(3), 2) --> (0,1), (0,2), (1,0), (1,2), (2,0), (2,1)");

static PyTypeObject permutations_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.permutations",                   /* tp_name */
    sizeof(permutationsobject),         /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)permutations_dealloc,           /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    permutations_doc,                           /* tp_doc */
    (traverseproc)permutations_traverse,        /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)permutations_next,            /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    permutations_new,                           /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* compress object ************************************************************/

/* Equivalent to:

    def compress(data, selectors):
        "compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F"
        return (d for d, s in zip(data, selectors) if s)
*/

typedef struct {
    PyObject_HEAD
    PyObject *data;
    PyObject *selectors;
} compressobject;

static PyTypeObject compress_type;

static PyObject *
compress_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *seq1, *seq2;
    PyObject *data=NULL, *selectors=NULL;
    compressobject *lz;
    static char *kwargs[] = {"data", "selectors", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "OO:compress", kwargs, &seq1, &seq2))
        return NULL;

    data = PyObject_GetIter(seq1);
    if (data == NULL)
        goto fail;
    selectors = PyObject_GetIter(seq2);
    if (selectors == NULL)
        goto fail;

    /* create compressobject structure */
    lz = (compressobject *)type->tp_alloc(type, 0);
    if (lz == NULL)
        goto fail;
    lz->data = data;
    lz->selectors = selectors;
    return (PyObject *)lz;

fail:
    Py_XDECREF(data);
    Py_XDECREF(selectors);
    return NULL;
}

static void
compress_dealloc(compressobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->data);
    Py_XDECREF(lz->selectors);
    Py_TYPE(lz)->tp_free(lz);
}

static int
compress_traverse(compressobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->data);
    Py_VISIT(lz->selectors);
    return 0;
}

static PyObject *
compress_next(compressobject *lz)
{
    PyObject *data = lz->data, *selectors = lz->selectors;
    PyObject *datum, *selector;
    PyObject *(*datanext)(PyObject *) = *Py_TYPE(data)->tp_iternext;
    PyObject *(*selectornext)(PyObject *) = *Py_TYPE(selectors)->tp_iternext;
    int ok;

    while (1) {
        /* Steps:  get datum, get selector, evaluate selector.
           Order is important (to match the pure python version
           in terms of which input gets a chance to raise an
           exception first).
        */

        datum = datanext(data);
        if (datum == NULL)
            return NULL;

        selector = selectornext(selectors);
        if (selector == NULL) {
            Py_DECREF(datum);
            return NULL;
        }

        ok = PyObject_IsTrue(selector);
        Py_DECREF(selector);
        if (ok == 1)
            return datum;
        Py_DECREF(datum);
        if (ok == -1)
            return NULL;
    }
}

PyDoc_STRVAR(compress_doc,
"compress(data, selectors) --> iterator over selected data\n\
\n\
Return data elements corresponding to true selector elements.\n\
Forms a shorter iterator from selected data elements using the\n\
selectors to choose the data elements.");

static PyTypeObject compress_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.compress",               /* tp_name */
    sizeof(compressobject),             /* tp_basicsize */
    0,                                                          /* tp_itemsize */
    /* methods */
    (destructor)compress_dealloc,       /* tp_dealloc */
    0,                                                                  /* tp_print */
    0,                                                                  /* tp_getattr */
    0,                                                                  /* tp_setattr */
    0,                                                                  /* tp_reserved */
    0,                                                                  /* tp_repr */
    0,                                                                  /* tp_as_number */
    0,                                                                  /* tp_as_sequence */
    0,                                                                  /* tp_as_mapping */
    0,                                                                  /* tp_hash */
    0,                                                                  /* tp_call */
    0,                                                                  /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                                                  /* tp_setattro */
    0,                                                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,                    /* tp_flags */
    compress_doc,                                       /* tp_doc */
    (traverseproc)compress_traverse,            /* tp_traverse */
    0,                                                                  /* tp_clear */
    0,                                                                  /* tp_richcompare */
    0,                                                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                                  /* tp_iter */
    (iternextfunc)compress_next,        /* tp_iternext */
    0,                                                                  /* tp_methods */
    0,                                                                  /* tp_members */
    0,                                                                  /* tp_getset */
    0,                                                                  /* tp_base */
    0,                                                                  /* tp_dict */
    0,                                                                  /* tp_descr_get */
    0,                                                                  /* tp_descr_set */
    0,                                                                  /* tp_dictoffset */
    0,                                                                  /* tp_init */
    0,                                                                  /* tp_alloc */
    compress_new,                                       /* tp_new */
    PyObject_GC_Del,                                    /* tp_free */
};


/* filterfalse object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *func;
    PyObject *it;
} filterfalseobject;

static PyTypeObject filterfalse_type;

static PyObject *
filterfalse_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *func, *seq;
    PyObject *it;
    filterfalseobject *lz;

    if (type == &filterfalse_type &&
        !_PyArg_NoKeywords("filterfalse()", kwds))
        return NULL;

    if (!PyArg_UnpackTuple(args, "filterfalse", 2, 2, &func, &seq))
        return NULL;

    /* Get iterator. */
    it = PyObject_GetIter(seq);
    if (it == NULL)
        return NULL;

    /* create filterfalseobject structure */
    lz = (filterfalseobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(it);
        return NULL;
    }
    Py_INCREF(func);
    lz->func = func;
    lz->it = it;

    return (PyObject *)lz;
}

static void
filterfalse_dealloc(filterfalseobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->func);
    Py_XDECREF(lz->it);
    Py_TYPE(lz)->tp_free(lz);
}

static int
filterfalse_traverse(filterfalseobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->it);
    Py_VISIT(lz->func);
    return 0;
}

static PyObject *
filterfalse_next(filterfalseobject *lz)
{
    PyObject *item;
    PyObject *it = lz->it;
    long ok;
    PyObject *(*iternext)(PyObject *);

    iternext = *Py_TYPE(it)->tp_iternext;
    for (;;) {
        item = iternext(it);
        if (item == NULL)
            return NULL;

        if (lz->func == Py_None || lz->func == (PyObject *)&PyBool_Type) {
            ok = PyObject_IsTrue(item);
        } else {
            PyObject *good;
            good = PyObject_CallFunctionObjArgs(lz->func,
                                                item, NULL);
            if (good == NULL) {
                Py_DECREF(item);
                return NULL;
            }
            ok = PyObject_IsTrue(good);
            Py_DECREF(good);
        }
        if (!ok)
            return item;
        Py_DECREF(item);
    }
}

PyDoc_STRVAR(filterfalse_doc,
"filterfalse(function or None, sequence) --> filterfalse object\n\
\n\
Return those items of sequence for which function(item) is false.\n\
If function is None, return the items that are false.");

static PyTypeObject filterfalse_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.filterfalse",            /* tp_name */
    sizeof(filterfalseobject),          /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)filterfalse_dealloc,            /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    filterfalse_doc,                    /* tp_doc */
    (traverseproc)filterfalse_traverse,         /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)filterfalse_next,     /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    filterfalse_new,                    /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* count object ************************************************************/

typedef struct {
    PyObject_HEAD
    Py_ssize_t cnt;
    PyObject *long_cnt;
    PyObject *long_step;
} countobject;

/* Counting logic and invariants:

fast_mode:  when cnt an integer < PY_SSIZE_T_MAX and no step is specified.

    assert(cnt != PY_SSIZE_T_MAX && long_cnt == NULL && long_step==PyInt(1));
    Advances with:  cnt += 1
    When count hits Y_SSIZE_T_MAX, switch to slow_mode.

slow_mode:  when cnt == PY_SSIZE_T_MAX, step is not int(1), or cnt is a float.

    assert(cnt == PY_SSIZE_T_MAX && long_cnt != NULL && long_step != NULL);
    All counting is done with python objects (no overflows or underflows).
    Advances with:  long_cnt += long_step
    Step may be zero -- effectively a slow version of repeat(cnt).
    Either long_cnt or long_step may be a float, Fraction, or Decimal.
*/

static PyTypeObject count_type;

static PyObject *
count_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    countobject *lz;
    int slow_mode = 0;
    Py_ssize_t cnt = 0;
    PyObject *long_cnt = NULL;
    PyObject *long_step = NULL;
    static char *kwlist[] = {"start", "step", 0};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OO:count",
                    kwlist, &long_cnt, &long_step))
        return NULL;

    if ((long_cnt != NULL && !PyNumber_Check(long_cnt)) ||
        (long_step != NULL && !PyNumber_Check(long_step))) {
                    PyErr_SetString(PyExc_TypeError, "a number is required");
                    return NULL;
    }

    if (long_cnt != NULL) {
        cnt = PyLong_AsSsize_t(long_cnt);
        if ((cnt == -1 && PyErr_Occurred()) || !PyLong_Check(long_cnt)) {
            PyErr_Clear();
            slow_mode = 1;
        }
        Py_INCREF(long_cnt);
    } else {
        cnt = 0;
        long_cnt = PyLong_FromLong(0);
    }

    /* If not specified, step defaults to 1 */
    if (long_step == NULL) {
        long_step = PyLong_FromLong(1);
        if (long_step == NULL) {
            Py_DECREF(long_cnt);
            return NULL;
        }
    } else
        Py_INCREF(long_step);

    assert(long_cnt != NULL && long_step != NULL);

    /* Fast mode only works when the step is 1 */
    if (!PyLong_Check(long_step) ||
        PyLong_AS_LONG(long_step) != 1) {
            slow_mode = 1;
    }

    if (slow_mode)
        cnt = PY_SSIZE_T_MAX;
    else
        Py_CLEAR(long_cnt);

    assert((cnt != PY_SSIZE_T_MAX && long_cnt == NULL && !slow_mode) ||
           (cnt == PY_SSIZE_T_MAX && long_cnt != NULL && slow_mode));
    assert(slow_mode ||
           (PyLong_Check(long_step) && PyLong_AS_LONG(long_step) == 1));

    /* create countobject structure */
    lz = (countobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_XDECREF(long_cnt);
        return NULL;
    }
    lz->cnt = cnt;
    lz->long_cnt = long_cnt;
    lz->long_step = long_step;

    return (PyObject *)lz;
}

static void
count_dealloc(countobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->long_cnt);
    Py_XDECREF(lz->long_step);
    Py_TYPE(lz)->tp_free(lz);
}

static int
count_traverse(countobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->long_cnt);
    Py_VISIT(lz->long_step);
    return 0;
}

static PyObject *
count_nextlong(countobject *lz)
{
    PyObject *long_cnt;
    PyObject *stepped_up;

    long_cnt = lz->long_cnt;
    if (long_cnt == NULL) {
        /* Switch to slow_mode */
        long_cnt = PyLong_FromSsize_t(PY_SSIZE_T_MAX);
        if (long_cnt == NULL)
            return NULL;
    }
    assert(lz->cnt == PY_SSIZE_T_MAX && long_cnt != NULL);

    stepped_up = PyNumber_Add(long_cnt, lz->long_step);
    if (stepped_up == NULL)
        return NULL;
    lz->long_cnt = stepped_up;
    return long_cnt;
}

static PyObject *
count_next(countobject *lz)
{
    if (lz->cnt == PY_SSIZE_T_MAX)
        return count_nextlong(lz);
    return PyLong_FromSsize_t(lz->cnt++);
}

static PyObject *
count_repr(countobject *lz)
{
    if (lz->cnt != PY_SSIZE_T_MAX)
        return PyUnicode_FromFormat("count(%zd)", lz->cnt);

    if (PyLong_Check(lz->long_step)) {
        long step = PyLong_AsLong(lz->long_step);
        if (step == -1 && PyErr_Occurred()) {
            PyErr_Clear();
        }
        if (step == 1) {
            /* Don't display step when it is an integer equal to 1 */
            return PyUnicode_FromFormat("count(%R)", lz->long_cnt);
        }
    }
    return PyUnicode_FromFormat("count(%R, %R)",
                                                            lz->long_cnt, lz->long_step);
}

static PyObject *
count_reduce(countobject *lz)
{
    if (lz->cnt == PY_SSIZE_T_MAX)
        return Py_BuildValue("O(OO)", Py_TYPE(lz), lz->long_cnt, lz->long_step);
    return Py_BuildValue("O(n)", Py_TYPE(lz), lz->cnt);
}

PyDoc_STRVAR(count_reduce_doc, "Return state information for pickling.");

static PyMethodDef count_methods[] = {
    {"__reduce__",      (PyCFunction)count_reduce,      METH_NOARGS,
     count_reduce_doc},
    {NULL,              NULL}   /* sentinel */
};

PyDoc_STRVAR(count_doc,
                         "count(start=0, step=1) --> count object\n\
\n\
Return a count object whose .__next__() method returns consecutive values.\n\
Equivalent to:\n\n\
    def count(firstval=0, step=1):\n\
    x = firstval\n\
    while 1:\n\
        yield x\n\
        x += step\n");

static PyTypeObject count_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.count",                  /* tp_name */
    sizeof(countobject),                /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)count_dealloc,          /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    (reprfunc)count_repr,               /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,                    /* tp_flags */
    count_doc,                          /* tp_doc */
    (traverseproc)count_traverse,                               /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)count_next,           /* tp_iternext */
    count_methods,                              /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    count_new,                          /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};


/* repeat object ************************************************************/

typedef struct {
    PyObject_HEAD
    PyObject *element;
    Py_ssize_t cnt;
} repeatobject;

static PyTypeObject repeat_type;

static PyObject *
repeat_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    repeatobject *ro;
    PyObject *element;
    Py_ssize_t cnt = -1;
    static char *kwargs[] = {"object", "times", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|n:repeat", kwargs,
                                     &element, &cnt))
        return NULL;

    if (PyTuple_Size(args) == 2 && cnt < 0)
        cnt = 0;

    ro = (repeatobject *)type->tp_alloc(type, 0);
    if (ro == NULL)
        return NULL;
    Py_INCREF(element);
    ro->element = element;
    ro->cnt = cnt;
    return (PyObject *)ro;
}

static void
repeat_dealloc(repeatobject *ro)
{
    PyObject_GC_UnTrack(ro);
    Py_XDECREF(ro->element);
    Py_TYPE(ro)->tp_free(ro);
}

static int
repeat_traverse(repeatobject *ro, visitproc visit, void *arg)
{
    Py_VISIT(ro->element);
    return 0;
}

static PyObject *
repeat_next(repeatobject *ro)
{
    if (ro->cnt == 0)
        return NULL;
    if (ro->cnt > 0)
        ro->cnt--;
    Py_INCREF(ro->element);
    return ro->element;
}

static PyObject *
repeat_repr(repeatobject *ro)
{
    if (ro->cnt == -1)
        return PyUnicode_FromFormat("repeat(%R)", ro->element);
    else
        return PyUnicode_FromFormat("repeat(%R, %zd)", ro->element, ro->cnt);
}

static PyObject *
repeat_len(repeatobject *ro)
{
    if (ro->cnt == -1) {
        PyErr_SetString(PyExc_TypeError, "len() of unsized object");
        return NULL;
    }
    return PyLong_FromSize_t(ro->cnt);
}

PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(it)).");

static PyMethodDef repeat_methods[] = {
    {"__length_hint__", (PyCFunction)repeat_len, METH_NOARGS, length_hint_doc},
    {NULL,              NULL}           /* sentinel */
};

PyDoc_STRVAR(repeat_doc,
"repeat(object [,times]) -> create an iterator which returns the object\n\
for the specified number of times.  If not specified, returns the object\n\
endlessly.");

static PyTypeObject repeat_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.repeat",                 /* tp_name */
    sizeof(repeatobject),               /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)repeat_dealloc,         /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    (reprfunc)repeat_repr,              /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    repeat_doc,                         /* tp_doc */
    (traverseproc)repeat_traverse,      /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)repeat_next,          /* tp_iternext */
    repeat_methods,                     /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    repeat_new,                         /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};

/* ziplongest object ************************************************************/

#include "Python.h"

typedef struct {
    PyObject_HEAD
    Py_ssize_t tuplesize;
    Py_ssize_t numactive;
    PyObject *ittuple;                  /* tuple of iterators */
    PyObject *result;
    PyObject *fillvalue;
} ziplongestobject;

static PyTypeObject ziplongest_type;

static PyObject *
zip_longest_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    ziplongestobject *lz;
    Py_ssize_t i;
    PyObject *ittuple;  /* tuple of iterators */
    PyObject *result;
    PyObject *fillvalue = Py_None;
    Py_ssize_t tuplesize = PySequence_Length(args);

    if (kwds != NULL && PyDict_CheckExact(kwds) && PyDict_Size(kwds) > 0) {
        fillvalue = PyDict_GetItemString(kwds, "fillvalue");
        if (fillvalue == NULL  ||  PyDict_Size(kwds) > 1) {
            PyErr_SetString(PyExc_TypeError,
                "zip_longest() got an unexpected keyword argument");
            return NULL;
        }
    }

    /* args must be a tuple */
    assert(PyTuple_Check(args));

    /* obtain iterators */
    ittuple = PyTuple_New(tuplesize);
    if (ittuple == NULL)
        return NULL;
    for (i=0; i < tuplesize; ++i) {
        PyObject *item = PyTuple_GET_ITEM(args, i);
        PyObject *it = PyObject_GetIter(item);
        if (it == NULL) {
            if (PyErr_ExceptionMatches(PyExc_TypeError))
                PyErr_Format(PyExc_TypeError,
                    "zip_longest argument #%zd must support iteration",
                    i+1);
            Py_DECREF(ittuple);
            return NULL;
        }
        PyTuple_SET_ITEM(ittuple, i, it);
    }

    /* create a result holder */
    result = PyTuple_New(tuplesize);
    if (result == NULL) {
        Py_DECREF(ittuple);
        return NULL;
    }
    for (i=0 ; i < tuplesize ; i++) {
        Py_INCREF(Py_None);
        PyTuple_SET_ITEM(result, i, Py_None);
    }

    /* create ziplongestobject structure */
    lz = (ziplongestobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(ittuple);
        Py_DECREF(result);
        return NULL;
    }
    lz->ittuple = ittuple;
    lz->tuplesize = tuplesize;
    lz->numactive = tuplesize;
    lz->result = result;
    Py_INCREF(fillvalue);
    lz->fillvalue = fillvalue;
    return (PyObject *)lz;
}

static void
zip_longest_dealloc(ziplongestobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->ittuple);
    Py_XDECREF(lz->result);
    Py_XDECREF(lz->fillvalue);
    Py_TYPE(lz)->tp_free(lz);
}

static int
zip_longest_traverse(ziplongestobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->ittuple);
    Py_VISIT(lz->result);
    Py_VISIT(lz->fillvalue);
    return 0;
}

static PyObject *
zip_longest_next(ziplongestobject *lz)
{
    Py_ssize_t i;
    Py_ssize_t tuplesize = lz->tuplesize;
    PyObject *result = lz->result;
    PyObject *it;
    PyObject *item;
    PyObject *olditem;

    if (tuplesize == 0)
        return NULL;
    if (lz->numactive == 0)
        return NULL;
    if (Py_REFCNT(result) == 1) {
        Py_INCREF(result);
        for (i=0 ; i < tuplesize ; i++) {
            it = PyTuple_GET_ITEM(lz->ittuple, i);
            if (it == NULL) {
                Py_INCREF(lz->fillvalue);
                item = lz->fillvalue;
            } else {
                item = PyIter_Next(it);
                if (item == NULL) {
                    lz->numactive -= 1;
                    if (lz->numactive == 0 || PyErr_Occurred()) {
                        lz->numactive = 0;
                        Py_DECREF(result);
                        return NULL;
                    } else {
                        Py_INCREF(lz->fillvalue);
                        item = lz->fillvalue;
                        PyTuple_SET_ITEM(lz->ittuple, i, NULL);
                        Py_DECREF(it);
                    }
                }
            }
            olditem = PyTuple_GET_ITEM(result, i);
            PyTuple_SET_ITEM(result, i, item);
            Py_DECREF(olditem);
        }
    } else {
        result = PyTuple_New(tuplesize);
        if (result == NULL)
            return NULL;
        for (i=0 ; i < tuplesize ; i++) {
            it = PyTuple_GET_ITEM(lz->ittuple, i);
            if (it == NULL) {
                Py_INCREF(lz->fillvalue);
                item = lz->fillvalue;
            } else {
                item = PyIter_Next(it);
                if (item == NULL) {
                    lz->numactive -= 1;
                    if (lz->numactive == 0 || PyErr_Occurred()) {
                        lz->numactive = 0;
                        Py_DECREF(result);
                        return NULL;
                    } else {
                        Py_INCREF(lz->fillvalue);
                        item = lz->fillvalue;
                        PyTuple_SET_ITEM(lz->ittuple, i, NULL);
                        Py_DECREF(it);
                    }
                }
            }
            PyTuple_SET_ITEM(result, i, item);
        }
    }
    return result;
}

PyDoc_STRVAR(zip_longest_doc,
"zip_longest(iter1 [,iter2 [...]], [fillvalue=None]) --> zip_longest object\n\
\n\
Return an zip_longest object whose .__next__() method returns a tuple where\n\
the i-th element comes from the i-th iterable argument.  The .__next__()\n\
method continues until the longest iterable in the argument sequence\n\
is exhausted and then it raises StopIteration.  When the shorter iterables\n\
are exhausted, the fillvalue is substituted in their place.  The fillvalue\n\
defaults to None or can be specified by a keyword argument.\n\
");

static PyTypeObject ziplongest_type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "itertools.zip_longest",            /* tp_name */
    sizeof(ziplongestobject),           /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)zip_longest_dealloc,            /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    zip_longest_doc,                            /* tp_doc */
    (traverseproc)zip_longest_traverse,    /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)zip_longest_next,     /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    zip_longest_new,                            /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};

/* module level code ********************************************************/

PyDoc_STRVAR(module_doc,
"Functional tools for creating and using iterators.\n\
\n\
Infinite iterators:\n\
count([n]) --> n, n+1, n+2, ...\n\
cycle(p) --> p0, p1, ... plast, p0, p1, ...\n\
repeat(elem [,n]) --> elem, elem, elem, ... endlessly or up to n times\n\
\n\
Iterators terminating on the shortest input sequence:\n\
chain(p, q, ...) --> p0, p1, ... plast, q0, q1, ... \n\
compress(data, selectors) --> (d[0] if s[0]), (d[1] if s[1]), ...\n\
dropwhile(pred, seq) --> seq[n], seq[n+1], starting when pred fails\n\
groupby(iterable[, keyfunc]) --> sub-iterators grouped by value of keyfunc(v)\n\
filterfalse(pred, seq) --> elements of seq where pred(elem) is False\n\
islice(seq, [start,] stop [, step]) --> elements from\n\
       seq[start:stop:step]\n\
starmap(fun, seq) --> fun(*seq[0]), fun(*seq[1]), ...\n\
tee(it, n=2) --> (it1, it2 , ... itn) splits one iterator into n\n\
takewhile(pred, seq) --> seq[0], seq[1], until pred fails\n\
zip_longest(p, q, ...) --> (p[0], q[0]), (p[1], q[1]), ... \n\
\n\
Combinatoric generators:\n\
product(p, q, ... [repeat=1]) --> cartesian product\n\
permutations(p[, r])\n\
combinations(p, r)\n\
combinations_with_replacement(p, r)\n\
");


static PyMethodDef module_methods[] = {
    {"tee",     (PyCFunction)tee,       METH_VARARGS, tee_doc},
    {NULL,              NULL}           /* sentinel */
};


static struct PyModuleDef itertoolsmodule = {
    PyModuleDef_HEAD_INIT,
    "itertools",
    module_doc,
    -1,
    module_methods,
    NULL,
    NULL,
    NULL,
    NULL
};

PyMODINIT_FUNC
PyInit_itertools(void)
{
    int i;
    PyObject *m;
    char *name;
    PyTypeObject *typelist[] = {
        &combinations_type,
        &cwr_type,
        &cycle_type,
        &dropwhile_type,
        &takewhile_type,
        &islice_type,
        &starmap_type,
        &chain_type,
        &compress_type,
        &filterfalse_type,
        &count_type,
        &ziplongest_type,
        &permutations_type,
        &product_type,
        &repeat_type,
        &groupby_type,
        NULL
    };

    Py_TYPE(&teedataobject_type) = &PyType_Type;
    m = PyModule_Create(&itertoolsmodule);
    if (m == NULL)
        return NULL;

    for (i=0 ; typelist[i] != NULL ; i++) {
        if (PyType_Ready(typelist[i]) < 0)
            return NULL;
        name = strchr(typelist[i]->tp_name, '.');
        assert (name != NULL);
        Py_INCREF(typelist[i]);
        PyModule_AddObject(m, name+1, (PyObject *)typelist[i]);
    }

    if (PyType_Ready(&teedataobject_type) < 0)
        return NULL;
    if (PyType_Ready(&tee_type) < 0)
        return NULL;
    if (PyType_Ready(&_grouper_type) < 0)
        return NULL;
    return m;
}