tupleobject.c 28.7 KB
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/* Tuple object implementation */

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#include "Python.h"
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/* Speed optimization to avoid frequent malloc/free of small tuples */
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#ifndef PyTuple_MAXSAVESIZE
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#define PyTuple_MAXSAVESIZE     20  /* Largest tuple to save on free list */
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#endif
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#ifndef PyTuple_MAXFREELIST
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#define PyTuple_MAXFREELIST  2000  /* Maximum number of tuples of each size to save */
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#endif

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#if PyTuple_MAXSAVESIZE > 0
/* Entries 1 up to PyTuple_MAXSAVESIZE are free lists, entry 0 is the empty
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   tuple () of which at most one instance will be allocated.
*/
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static PyTupleObject *free_list[PyTuple_MAXSAVESIZE];
static int numfree[PyTuple_MAXSAVESIZE];
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#endif
#ifdef COUNT_ALLOCS
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Py_ssize_t fast_tuple_allocs;
Py_ssize_t tuple_zero_allocs;
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#endif

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/* Debug statistic to count GC tracking of tuples.
   Please note that tuples are only untracked when considered by the GC, and
   many of them will be dead before. Therefore, a tracking rate close to 100%
   does not necessarily prove that the heuristic is inefficient.
*/
#ifdef SHOW_TRACK_COUNT
static Py_ssize_t count_untracked = 0;
static Py_ssize_t count_tracked = 0;

static void
show_track(void)
{
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    fprintf(stderr, "Tuples created: %" PY_FORMAT_SIZE_T "d\n",
        count_tracked + count_untracked);
    fprintf(stderr, "Tuples tracked by the GC: %" PY_FORMAT_SIZE_T
        "d\n", count_tracked);
    fprintf(stderr, "%.2f%% tuple tracking rate\n\n",
        (100.0*count_tracked/(count_untracked+count_tracked)));
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}
#endif


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PyObject *
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PyTuple_New(register Py_ssize_t size)
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{
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    register PyTupleObject *op;
    Py_ssize_t i;
    if (size < 0) {
        PyErr_BadInternalCall();
        return NULL;
    }
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#if PyTuple_MAXSAVESIZE > 0
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    if (size == 0 && free_list[0]) {
        op = free_list[0];
        Py_INCREF(op);
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#ifdef COUNT_ALLOCS
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        tuple_zero_allocs++;
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#endif
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        return (PyObject *) op;
    }
    if (size < PyTuple_MAXSAVESIZE && (op = free_list[size]) != NULL) {
        free_list[size] = (PyTupleObject *) op->ob_item[0];
        numfree[size]--;
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#ifdef COUNT_ALLOCS
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        fast_tuple_allocs++;
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#endif
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        /* Inline PyObject_InitVar */
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#ifdef Py_TRACE_REFS
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        Py_SIZE(op) = size;
        Py_TYPE(op) = &PyTuple_Type;
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#endif
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        _Py_NewReference((PyObject *)op);
    }
    else
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#endif
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    {
        Py_ssize_t nbytes = size * sizeof(PyObject *);
        /* Check for overflow */
        if (nbytes / sizeof(PyObject *) != (size_t)size ||
            (nbytes > PY_SSIZE_T_MAX - sizeof(PyTupleObject) - sizeof(PyObject *)))
        {
            return PyErr_NoMemory();
        }
        nbytes += sizeof(PyTupleObject) - sizeof(PyObject *);

        op = PyObject_GC_NewVar(PyTupleObject, &PyTuple_Type, size);
        if (op == NULL)
            return NULL;
    }
    for (i=0; i < size; i++)
        op->ob_item[i] = NULL;
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#if PyTuple_MAXSAVESIZE > 0
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    if (size == 0) {
        free_list[0] = op;
        ++numfree[0];
        Py_INCREF(op);          /* extra INCREF so that this is never freed */
    }
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#endif
#ifdef SHOW_TRACK_COUNT
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    count_tracked++;
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#endif
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    _PyObject_GC_TRACK(op);
    return (PyObject *) op;
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}

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Py_ssize_t
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PyTuple_Size(register PyObject *op)
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{
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    if (!PyTuple_Check(op)) {
        PyErr_BadInternalCall();
        return -1;
    }
    else
        return Py_SIZE(op);
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}

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PyObject *
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PyTuple_GetItem(register PyObject *op, register Py_ssize_t i)
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{
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    if (!PyTuple_Check(op)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    if (i < 0 || i >= Py_SIZE(op)) {
        PyErr_SetString(PyExc_IndexError, "tuple index out of range");
        return NULL;
    }
    return ((PyTupleObject *)op) -> ob_item[i];
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}

int
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PyTuple_SetItem(register PyObject *op, register Py_ssize_t i, PyObject *newitem)
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{
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    register PyObject *olditem;
    register PyObject **p;
    if (!PyTuple_Check(op) || op->ob_refcnt != 1) {
        Py_XDECREF(newitem);
        PyErr_BadInternalCall();
        return -1;
    }
    if (i < 0 || i >= Py_SIZE(op)) {
        Py_XDECREF(newitem);
        PyErr_SetString(PyExc_IndexError,
                        "tuple assignment index out of range");
        return -1;
    }
    p = ((PyTupleObject *)op) -> ob_item + i;
    olditem = *p;
    *p = newitem;
    Py_XDECREF(olditem);
    return 0;
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}

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void
_PyTuple_MaybeUntrack(PyObject *op)
{
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    PyTupleObject *t;
    Py_ssize_t i, n;

    if (!PyTuple_CheckExact(op) || !_PyObject_GC_IS_TRACKED(op))
        return;
    t = (PyTupleObject *) op;
    n = Py_SIZE(t);
    for (i = 0; i < n; i++) {
        PyObject *elt = PyTuple_GET_ITEM(t, i);
        /* Tuple with NULL elements aren't
           fully constructed, don't untrack
           them yet. */
        if (!elt ||
            _PyObject_GC_MAY_BE_TRACKED(elt))
            return;
    }
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#ifdef SHOW_TRACK_COUNT
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    count_tracked--;
    count_untracked++;
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#endif
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    _PyObject_GC_UNTRACK(op);
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}

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PyObject *
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PyTuple_Pack(Py_ssize_t n, ...)
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{
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    Py_ssize_t i;
    PyObject *o;
    PyObject *result;
    PyObject **items;
    va_list vargs;

    va_start(vargs, n);
    result = PyTuple_New(n);
    if (result == NULL)
        return NULL;
    items = ((PyTupleObject *)result)->ob_item;
    for (i = 0; i < n; i++) {
        o = va_arg(vargs, PyObject *);
        Py_INCREF(o);
        items[i] = o;
    }
    va_end(vargs);
    return result;
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}


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/* Methods */

static void
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tupledealloc(register PyTupleObject *op)
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{
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    register Py_ssize_t i;
    register Py_ssize_t len =  Py_SIZE(op);
    PyObject_GC_UnTrack(op);
    Py_TRASHCAN_SAFE_BEGIN(op)
    if (len > 0) {
        i = len;
        while (--i >= 0)
            Py_XDECREF(op->ob_item[i]);
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#if PyTuple_MAXSAVESIZE > 0
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        if (len < PyTuple_MAXSAVESIZE &&
            numfree[len] < PyTuple_MAXFREELIST &&
            Py_TYPE(op) == &PyTuple_Type)
        {
            op->ob_item[0] = (PyObject *) free_list[len];
            numfree[len]++;
            free_list[len] = op;
            goto done; /* return */
        }
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#endif
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    }
    Py_TYPE(op)->tp_free((PyObject *)op);
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done:
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    Py_TRASHCAN_SAFE_END(op)
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}

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static PyObject *
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tuplerepr(PyTupleObject *v)
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{
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    Py_ssize_t i, n;
    PyObject *s, *temp;
    PyObject *pieces, *result = NULL;

    n = Py_SIZE(v);
    if (n == 0)
        return PyUnicode_FromString("()");

    /* While not mutable, it is still possible to end up with a cycle in a
       tuple through an object that stores itself within a tuple (and thus
       infinitely asks for the repr of itself). This should only be
       possible within a type. */
    i = Py_ReprEnter((PyObject *)v);
    if (i != 0) {
        return i > 0 ? PyUnicode_FromString("(...)") : NULL;
    }

    pieces = PyTuple_New(n);
    if (pieces == NULL)
        return NULL;

    /* Do repr() on each element. */
    for (i = 0; i < n; ++i) {
        if (Py_EnterRecursiveCall(" while getting the repr of a tuple"))
            goto Done;
        s = PyObject_Repr(v->ob_item[i]);
        Py_LeaveRecursiveCall();
        if (s == NULL)
            goto Done;
        PyTuple_SET_ITEM(pieces, i, s);
    }

    /* Add "()" decorations to the first and last items. */
    assert(n > 0);
    s = PyUnicode_FromString("(");
    if (s == NULL)
        goto Done;
    temp = PyTuple_GET_ITEM(pieces, 0);
    PyUnicode_AppendAndDel(&s, temp);
    PyTuple_SET_ITEM(pieces, 0, s);
    if (s == NULL)
        goto Done;

    s = PyUnicode_FromString(n == 1 ? ",)" : ")");
    if (s == NULL)
        goto Done;
    temp = PyTuple_GET_ITEM(pieces, n-1);
    PyUnicode_AppendAndDel(&temp, s);
    PyTuple_SET_ITEM(pieces, n-1, temp);
    if (temp == NULL)
        goto Done;

    /* Paste them all together with ", " between. */
    s = PyUnicode_FromString(", ");
    if (s == NULL)
        goto Done;
    result = PyUnicode_Join(s, pieces);
    Py_DECREF(s);
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Done:
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    Py_DECREF(pieces);
    Py_ReprLeave((PyObject *)v);
    return result;
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}

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/* The addend 82520, was selected from the range(0, 1000000) for
   generating the greatest number of prime multipliers for tuples
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   upto length eight:

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     1082527, 1165049, 1082531, 1165057, 1247581, 1330103, 1082533,
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     1330111, 1412633, 1165069, 1247599, 1495177, 1577699
*/

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static Py_hash_t
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tuplehash(PyTupleObject *v)
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{
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    register Py_hash_t x, y;
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    register Py_ssize_t len = Py_SIZE(v);
    register PyObject **p;
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    Py_hash_t mult = 1000003L;
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    x = 0x345678L;
    p = v->ob_item;
    while (--len >= 0) {
        y = PyObject_Hash(*p++);
        if (y == -1)
            return -1;
        x = (x ^ y) * mult;
        /* the cast might truncate len; that doesn't change hash stability */
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        mult += (Py_hash_t)(82520L + len + len);
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    }
    x += 97531L;
    if (x == -1)
        x = -2;
    return x;
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}

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static Py_ssize_t
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tuplelength(PyTupleObject *a)
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{
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    return Py_SIZE(a);
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}

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static int
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tuplecontains(PyTupleObject *a, PyObject *el)
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{
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    Py_ssize_t i;
    int cmp;
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    for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i)
        cmp = PyObject_RichCompareBool(el, PyTuple_GET_ITEM(a, i),
                                           Py_EQ);
    return cmp;
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}

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static PyObject *
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tupleitem(register PyTupleObject *a, register Py_ssize_t i)
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{
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    if (i < 0 || i >= Py_SIZE(a)) {
        PyErr_SetString(PyExc_IndexError, "tuple index out of range");
        return NULL;
    }
    Py_INCREF(a->ob_item[i]);
    return a->ob_item[i];
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}

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static PyObject *
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tupleslice(register PyTupleObject *a, register Py_ssize_t ilow,
           register Py_ssize_t ihigh)
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{
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    register PyTupleObject *np;
    PyObject **src, **dest;
    register Py_ssize_t i;
    Py_ssize_t len;
    if (ilow < 0)
        ilow = 0;
    if (ihigh > Py_SIZE(a))
        ihigh = Py_SIZE(a);
    if (ihigh < ilow)
        ihigh = ilow;
    if (ilow == 0 && ihigh == Py_SIZE(a) && PyTuple_CheckExact(a)) {
        Py_INCREF(a);
        return (PyObject *)a;
    }
    len = ihigh - ilow;
    np = (PyTupleObject *)PyTuple_New(len);
    if (np == NULL)
        return NULL;
    src = a->ob_item + ilow;
    dest = np->ob_item;
    for (i = 0; i < len; i++) {
        PyObject *v = src[i];
        Py_INCREF(v);
        dest[i] = v;
    }
    return (PyObject *)np;
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}

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PyObject *
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PyTuple_GetSlice(PyObject *op, Py_ssize_t i, Py_ssize_t j)
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{
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    if (op == NULL || !PyTuple_Check(op)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    return tupleslice((PyTupleObject *)op, i, j);
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}

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static PyObject *
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tupleconcat(register PyTupleObject *a, register PyObject *bb)
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{
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    register Py_ssize_t size;
    register Py_ssize_t i;
    PyObject **src, **dest;
    PyTupleObject *np;
    if (!PyTuple_Check(bb)) {
        PyErr_Format(PyExc_TypeError,
             "can only concatenate tuple (not \"%.200s\") to tuple",
                 Py_TYPE(bb)->tp_name);
        return NULL;
    }
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#define b ((PyTupleObject *)bb)
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    size = Py_SIZE(a) + Py_SIZE(b);
    if (size < 0)
        return PyErr_NoMemory();
    np = (PyTupleObject *) PyTuple_New(size);
    if (np == NULL) {
        return NULL;
    }
    src = a->ob_item;
    dest = np->ob_item;
    for (i = 0; i < Py_SIZE(a); i++) {
        PyObject *v = src[i];
        Py_INCREF(v);
        dest[i] = v;
    }
    src = b->ob_item;
    dest = np->ob_item + Py_SIZE(a);
    for (i = 0; i < Py_SIZE(b); i++) {
        PyObject *v = src[i];
        Py_INCREF(v);
        dest[i] = v;
    }
    return (PyObject *)np;
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#undef b
}

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static PyObject *
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tuplerepeat(PyTupleObject *a, Py_ssize_t n)
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{
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    Py_ssize_t i, j;
    Py_ssize_t size;
    PyTupleObject *np;
    PyObject **p, **items;
    if (n < 0)
        n = 0;
    if (Py_SIZE(a) == 0 || n == 1) {
        if (PyTuple_CheckExact(a)) {
            /* Since tuples are immutable, we can return a shared
               copy in this case */
            Py_INCREF(a);
            return (PyObject *)a;
        }
        if (Py_SIZE(a) == 0)
            return PyTuple_New(0);
    }
    size = Py_SIZE(a) * n;
    if (size/Py_SIZE(a) != n)
        return PyErr_NoMemory();
    np = (PyTupleObject *) PyTuple_New(size);
    if (np == NULL)
        return NULL;
    p = np->ob_item;
    items = a->ob_item;
    for (i = 0; i < n; i++) {
        for (j = 0; j < Py_SIZE(a); j++) {
            *p = items[j];
            Py_INCREF(*p);
            p++;
        }
    }
    return (PyObject *) np;
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}

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static PyObject *
tupleindex(PyTupleObject *self, PyObject *args)
{
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    Py_ssize_t i, start=0, stop=Py_SIZE(self);
    PyObject *v;

    if (!PyArg_ParseTuple(args, "O|O&O&:index", &v,
                                _PyEval_SliceIndex, &start,
                                _PyEval_SliceIndex, &stop))
        return NULL;
    if (start < 0) {
        start += Py_SIZE(self);
        if (start < 0)
            start = 0;
    }
    if (stop < 0) {
        stop += Py_SIZE(self);
        if (stop < 0)
            stop = 0;
    }
    for (i = start; i < stop && i < Py_SIZE(self); i++) {
        int cmp = PyObject_RichCompareBool(self->ob_item[i], v, Py_EQ);
        if (cmp > 0)
            return PyLong_FromSsize_t(i);
        else if (cmp < 0)
            return NULL;
    }
    PyErr_SetString(PyExc_ValueError, "tuple.index(x): x not in tuple");
    return NULL;
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}

static PyObject *
tuplecount(PyTupleObject *self, PyObject *v)
{
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    Py_ssize_t count = 0;
    Py_ssize_t i;

    for (i = 0; i < Py_SIZE(self); i++) {
        int cmp = PyObject_RichCompareBool(self->ob_item[i], v, Py_EQ);
        if (cmp > 0)
            count++;
        else if (cmp < 0)
            return NULL;
    }
    return PyLong_FromSsize_t(count);
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}

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static int
tupletraverse(PyTupleObject *o, visitproc visit, void *arg)
{
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    Py_ssize_t i;
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    for (i = Py_SIZE(o); --i >= 0; )
        Py_VISIT(o->ob_item[i]);
    return 0;
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}

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static PyObject *
tuplerichcompare(PyObject *v, PyObject *w, int op)
{
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    PyTupleObject *vt, *wt;
    Py_ssize_t i;
    Py_ssize_t vlen, wlen;

    if (!PyTuple_Check(v) || !PyTuple_Check(w)) {
        Py_INCREF(Py_NotImplemented);
        return Py_NotImplemented;
    }

    vt = (PyTupleObject *)v;
    wt = (PyTupleObject *)w;

    vlen = Py_SIZE(vt);
    wlen = Py_SIZE(wt);

    /* Note:  the corresponding code for lists has an "early out" test
     * here when op is EQ or NE and the lengths differ.  That pays there,
     * but Tim was unable to find any real code where EQ/NE tuple
     * compares don't have the same length, so testing for it here would
     * have cost without benefit.
     */

    /* Search for the first index where items are different.
     * Note that because tuples are immutable, it's safe to reuse
     * vlen and wlen across the comparison calls.
     */
    for (i = 0; i < vlen && i < wlen; i++) {
        int k = PyObject_RichCompareBool(vt->ob_item[i],
                                         wt->ob_item[i], Py_EQ);
        if (k < 0)
            return NULL;
        if (!k)
            break;
    }

    if (i >= vlen || i >= wlen) {
        /* No more items to compare -- compare sizes */
        int cmp;
        PyObject *res;
        switch (op) {
        case Py_LT: cmp = vlen <  wlen; break;
        case Py_LE: cmp = vlen <= wlen; break;
        case Py_EQ: cmp = vlen == wlen; break;
        case Py_NE: cmp = vlen != wlen; break;
        case Py_GT: cmp = vlen >  wlen; break;
        case Py_GE: cmp = vlen >= wlen; break;
        default: return NULL; /* cannot happen */
        }
        if (cmp)
            res = Py_True;
        else
            res = Py_False;
        Py_INCREF(res);
        return res;
    }

    /* We have an item that differs -- shortcuts for EQ/NE */
    if (op == Py_EQ) {
        Py_INCREF(Py_False);
        return Py_False;
    }
    if (op == Py_NE) {
        Py_INCREF(Py_True);
        return Py_True;
    }

    /* Compare the final item again using the proper operator */
    return PyObject_RichCompare(vt->ob_item[i], wt->ob_item[i], op);
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}

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static PyObject *
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tuple_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);

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static PyObject *
tuple_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
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    PyObject *arg = NULL;
    static char *kwlist[] = {"sequence", 0};

    if (type != &PyTuple_Type)
        return tuple_subtype_new(type, args, kwds);
    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|O:tuple", kwlist, &arg))
        return NULL;

    if (arg == NULL)
        return PyTuple_New(0);
    else
        return PySequence_Tuple(arg);
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}

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static PyObject *
tuple_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
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    PyObject *tmp, *newobj, *item;
    Py_ssize_t i, n;

    assert(PyType_IsSubtype(type, &PyTuple_Type));
    tmp = tuple_new(&PyTuple_Type, args, kwds);
    if (tmp == NULL)
        return NULL;
    assert(PyTuple_Check(tmp));
    newobj = type->tp_alloc(type, n = PyTuple_GET_SIZE(tmp));
    if (newobj == NULL)
        return NULL;
    for (i = 0; i < n; i++) {
        item = PyTuple_GET_ITEM(tmp, i);
        Py_INCREF(item);
        PyTuple_SET_ITEM(newobj, i, item);
    }
    Py_DECREF(tmp);
    return newobj;
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}

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PyDoc_STRVAR(tuple_doc,
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"tuple() -> empty tuple\n\
tuple(iterable) -> tuple initialized from iterable's items\n\
\n\
If the argument is a tuple, the return value is the same object.");
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static PySequenceMethods tuple_as_sequence = {
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    (lenfunc)tuplelength,                       /* sq_length */
    (binaryfunc)tupleconcat,                    /* sq_concat */
    (ssizeargfunc)tuplerepeat,                  /* sq_repeat */
    (ssizeargfunc)tupleitem,                    /* sq_item */
    0,                                          /* sq_slice */
    0,                                          /* sq_ass_item */
    0,                                          /* sq_ass_slice */
    (objobjproc)tuplecontains,                  /* sq_contains */
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};

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static PyObject*
tuplesubscript(PyTupleObject* self, PyObject* item)
{
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    if (PyIndex_Check(item)) {
        Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
        if (i == -1 && PyErr_Occurred())
            return NULL;
        if (i < 0)
            i += PyTuple_GET_SIZE(self);
        return tupleitem(self, i);
    }
    else if (PySlice_Check(item)) {
        Py_ssize_t start, stop, step, slicelength, cur, i;
        PyObject* result;
        PyObject* it;
        PyObject **src, **dest;

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        if (PySlice_GetIndicesEx(item,
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                         PyTuple_GET_SIZE(self),
                         &start, &stop, &step, &slicelength) < 0) {
            return NULL;
        }

        if (slicelength <= 0) {
            return PyTuple_New(0);
        }
        else if (start == 0 && step == 1 &&
                 slicelength == PyTuple_GET_SIZE(self) &&
                 PyTuple_CheckExact(self)) {
            Py_INCREF(self);
            return (PyObject *)self;
        }
        else {
            result = PyTuple_New(slicelength);
            if (!result) return NULL;

            src = self->ob_item;
            dest = ((PyTupleObject *)result)->ob_item;
            for (cur = start, i = 0; i < slicelength;
                 cur += step, i++) {
                it = src[cur];
                Py_INCREF(it);
                dest[i] = it;
            }

            return result;
        }
    }
    else {
        PyErr_Format(PyExc_TypeError,
                     "tuple indices must be integers, not %.200s",
                     Py_TYPE(item)->tp_name);
        return NULL;
    }
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}

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static PyObject *
tuple_getnewargs(PyTupleObject *v)
{
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    return Py_BuildValue("(N)", tupleslice(v, 0, Py_SIZE(v)));

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}

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static PyObject *
tuple_sizeof(PyTupleObject *self)
{
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    Py_ssize_t res;
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    res = PyTuple_Type.tp_basicsize + Py_SIZE(self) * sizeof(PyObject *);
    return PyLong_FromSsize_t(res);
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}

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PyDoc_STRVAR(index_doc,
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"T.index(value, [start, [stop]]) -> integer -- return first index of value.\n"
"Raises ValueError if the value is not present."
);
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PyDoc_STRVAR(count_doc,
"T.count(value) -> integer -- return number of occurrences of value");
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PyDoc_STRVAR(sizeof_doc,
"T.__sizeof__() -- size of T in memory, in bytes");
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static PyMethodDef tuple_methods[] = {
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    {"__getnewargs__",          (PyCFunction)tuple_getnewargs,  METH_NOARGS},
    {"__sizeof__",      (PyCFunction)tuple_sizeof, METH_NOARGS, sizeof_doc},
    {"index",           (PyCFunction)tupleindex,  METH_VARARGS, index_doc},
    {"count",           (PyCFunction)tuplecount,  METH_O, count_doc},
    {NULL,              NULL}           /* sentinel */
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};

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static PyMappingMethods tuple_as_mapping = {
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    (lenfunc)tuplelength,
    (binaryfunc)tuplesubscript,
    0
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};

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static PyObject *tuple_iter(PyObject *seq);

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PyTypeObject PyTuple_Type = {
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    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "tuple",
    sizeof(PyTupleObject) - sizeof(PyObject *),
    sizeof(PyObject *),
    (destructor)tupledealloc,                   /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    (reprfunc)tuplerepr,                        /* tp_repr */
    0,                                          /* tp_as_number */
    &tuple_as_sequence,                         /* tp_as_sequence */
    &tuple_as_mapping,                          /* tp_as_mapping */
    (hashfunc)tuplehash,                        /* 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 | Py_TPFLAGS_TUPLE_SUBCLASS, /* tp_flags */
    tuple_doc,                                  /* tp_doc */
    (traverseproc)tupletraverse,                /* tp_traverse */
    0,                                          /* tp_clear */
    tuplerichcompare,                           /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    tuple_iter,                                 /* tp_iter */
    0,                                          /* tp_iternext */
    tuple_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 */
    tuple_new,                                  /* tp_new */
    PyObject_GC_Del,                            /* tp_free */
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};
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/* The following function breaks the notion that tuples are immutable:
   it changes the size of a tuple.  We get away with this only if there
   is only one module referencing the object.  You can also think of it
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   as creating a new tuple object and destroying the old one, only more
   efficiently.  In any case, don't use this if the tuple may already be
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   known to some other part of the code. */
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int
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_PyTuple_Resize(PyObject **pv, Py_ssize_t newsize)
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{
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    register PyTupleObject *v;
    register PyTupleObject *sv;
    Py_ssize_t i;
    Py_ssize_t oldsize;

    v = (PyTupleObject *) *pv;
    if (v == NULL || Py_TYPE(v) != &PyTuple_Type ||
        (Py_SIZE(v) != 0 && Py_REFCNT(v) != 1)) {
        *pv = 0;
        Py_XDECREF(v);
        PyErr_BadInternalCall();
        return -1;
    }
    oldsize = Py_SIZE(v);
    if (oldsize == newsize)
        return 0;

    if (oldsize == 0) {
        /* Empty tuples are often shared, so we should never
           resize them in-place even if we do own the only
           (current) reference */
        Py_DECREF(v);
        *pv = PyTuple_New(newsize);
        return *pv == NULL ? -1 : 0;
    }

    /* XXX UNREF/NEWREF interface should be more symmetrical */
    _Py_DEC_REFTOTAL;
    if (_PyObject_GC_IS_TRACKED(v))
        _PyObject_GC_UNTRACK(v);
    _Py_ForgetReference((PyObject *) v);
    /* DECREF items deleted by shrinkage */
    for (i = newsize; i < oldsize; i++) {
        Py_XDECREF(v->ob_item[i]);
        v->ob_item[i] = NULL;
    }
    sv = PyObject_GC_Resize(PyTupleObject, v, newsize);
    if (sv == NULL) {
        *pv = NULL;
        PyObject_GC_Del(v);
        return -1;
    }
    _Py_NewReference((PyObject *) sv);
    /* Zero out items added by growing */
    if (newsize > oldsize)
        memset(&sv->ob_item[oldsize], 0,
               sizeof(*sv->ob_item) * (newsize - oldsize));
    *pv = (PyObject *) sv;
    _PyObject_GC_TRACK(sv);
    return 0;
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}
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int
PyTuple_ClearFreeList(void)
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{
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    int freelist_size = 0;
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#if PyTuple_MAXSAVESIZE > 0
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    int i;
    for (i = 1; i < PyTuple_MAXSAVESIZE; i++) {
        PyTupleObject *p, *q;
        p = free_list[i];
        freelist_size += numfree[i];
        free_list[i] = NULL;
        numfree[i] = 0;
        while (p) {
            q = p;
            p = (PyTupleObject *)(p->ob_item[0]);
            PyObject_GC_Del(q);
        }
    }
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#endif
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    return freelist_size;
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}
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void
PyTuple_Fini(void)
{
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    /* empty tuples are used all over the place and applications may
     * rely on the fact that an empty tuple is a singleton. */
    Py_XDECREF(free_list[0]);
    free_list[0] = NULL;
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    (void)PyTuple_ClearFreeList();
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#endif
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#ifdef SHOW_TRACK_COUNT
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    show_track();
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#endif
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}
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/*********************** Tuple Iterator **************************/

typedef struct {
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    PyObject_HEAD
    long it_index;
    PyTupleObject *it_seq; /* Set to NULL when iterator is exhausted */
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} tupleiterobject;

static void
tupleiter_dealloc(tupleiterobject *it)
{
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    _PyObject_GC_UNTRACK(it);
    Py_XDECREF(it->it_seq);
    PyObject_GC_Del(it);
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}

static int
tupleiter_traverse(tupleiterobject *it, visitproc visit, void *arg)
{
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    Py_VISIT(it->it_seq);
    return 0;
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}

static PyObject *
tupleiter_next(tupleiterobject *it)
{
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    PyTupleObject *seq;
    PyObject *item;

    assert(it != NULL);
    seq = it->it_seq;
    if (seq == NULL)
        return NULL;
    assert(PyTuple_Check(seq));

    if (it->it_index < PyTuple_GET_SIZE(seq)) {
        item = PyTuple_GET_ITEM(seq, it->it_index);
        ++it->it_index;
        Py_INCREF(item);
        return item;
    }

    Py_DECREF(seq);
    it->it_seq = NULL;
    return NULL;
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}

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static PyObject *
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tupleiter_len(tupleiterobject *it)
{
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    Py_ssize_t len = 0;
    if (it->it_seq)
        len = PyTuple_GET_SIZE(it->it_seq) - it->it_index;
    return PyLong_FromSsize_t(len);
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}

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PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(it)).");
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static PyMethodDef tupleiter_methods[] = {
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    {"__length_hint__", (PyCFunction)tupleiter_len, METH_NOARGS, length_hint_doc},
    {NULL,              NULL}           /* sentinel */
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};

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PyTypeObject PyTupleIter_Type = {
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    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "tuple_iterator",                           /* tp_name */
    sizeof(tupleiterobject),                    /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)tupleiter_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)tupleiter_traverse,           /* tp_traverse */
    0,                                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    PyObject_SelfIter,                          /* tp_iter */
    (iternextfunc)tupleiter_next,               /* tp_iternext */
    tupleiter_methods,                          /* tp_methods */
    0,
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};
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static PyObject *
tuple_iter(PyObject *seq)
{
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    tupleiterobject *it;

    if (!PyTuple_Check(seq)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    it = PyObject_GC_New(tupleiterobject, &PyTupleIter_Type);
    if (it == NULL)
        return NULL;
    it->it_index = 0;
    Py_INCREF(seq);
    it->it_seq = (PyTupleObject *)seq;
    _PyObject_GC_TRACK(it);
    return (PyObject *)it;
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}