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vstinner bpo-40521 : Always create the empty tuple singleton (GH-21116 )

Latest commit 0430dfa

Jun 24, 2020

Py_InitializeFromConfig() now always creates the empty tuple
singleton as soon as possible.

Optimize PyTuple_New(0): it no longer has to check if the empty tuple
was created or not, it is always creatd.

* Add tuple_create_empty_tuple_singleton() function.
* Add tuple_get_empty() function.
* Remove state parameter of tuple_alloc().

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	/* Tuple object implementation */

	#include "Python.h"
	#include "pycore_abstract.h" // _PyIndex_Check()
	#include "pycore_gc.h" // _PyObject_GC_IS_TRACKED()
	#include "pycore_initconfig.h" // _PyStatus_OK()
	#include "pycore_object.h" // _PyObject_GC_TRACK()

	/*[clinic input]
	class tuple "PyTupleObject *" "&PyTuple_Type"
	[clinic start generated code]*/
	/[clinic end generated code: output=da39a3ee5e6b4b0d input=f051ba3cfdf9a189]/

	#include "clinic/tupleobject.c.h"


	#if PyTuple_MAXSAVESIZE > 0
	static struct _Py_tuple_state *
	get_tuple_state(void)
	{
	PyInterpreterState *interp = _PyInterpreterState_GET();
	return &interp->tuple;
	}
	#endif


	static inline void
	tuple_gc_track(PyTupleObject *op)
	{
	_PyObject_GC_TRACK(op);
	}


	/* Print summary info about the state of the optimized allocator */
	void
	_PyTuple_DebugMallocStats(FILE *out)
	{
	#if PyTuple_MAXSAVESIZE > 0
	struct _Py_tuple_state *state = get_tuple_state();
	for (int i = 1; i < PyTuple_MAXSAVESIZE; i++) {
	char buf[128];
	PyOS_snprintf(buf, sizeof(buf),
	"free %d-sized PyTupleObject", i);
	_PyDebugAllocatorStats(out, buf, state->numfree[i],
	_PyObject_VAR_SIZE(&PyTuple_Type, i));
	}
	#endif
	}

	/* Allocate an uninitialized tuple object. Before making it public following
	steps must be done:
	- initialize its items
	- call tuple_gc_track() on it
	Because the empty tuple is always reused and it's already tracked by GC,
	this function must not be called with size == 0 (unless from PyTuple_New()
	which wraps this function).
	*/
	static PyTupleObject *
	tuple_alloc(Py_ssize_t size)
	{
	PyTupleObject *op;
	#if PyTuple_MAXSAVESIZE > 0
	// If Python is built with the empty tuple singleton,
	// tuple_alloc(0) must not be called.
	assert(size != 0);
	#endif
	if (size < 0) {
	PyErr_BadInternalCall();
	return NULL;
	}

	#if PyTuple_MAXSAVESIZE > 0
	struct _Py_tuple_state *state = get_tuple_state();
	#ifdef Py_DEBUG
	// tuple_alloc() must not be called after _PyTuple_Fini()
	assert(state->numfree[0] != -1);
	#endif
	if (size < PyTuple_MAXSAVESIZE && (op = state->free_list[size]) != NULL) {
	assert(size != 0);
	state->free_list[size] = (PyTupleObject *) op->ob_item[0];
	state->numfree[size]--;
	/* Inlined _PyObject_InitVar() without _PyType_HasFeature() test */
	#ifdef Py_TRACE_REFS
	Py_SET_SIZE(op, size);
	Py_SET_TYPE(op, &PyTuple_Type);
	#endif
	_Py_NewReference((PyObject *)op);
	}
	else
	#endif
	{
	/* Check for overflow */
	if ((size_t)size > ((size_t)PY_SSIZE_T_MAX - (sizeof(PyTupleObject) -
	sizeof(PyObject ))) / sizeof(PyObject )) {
	return (PyTupleObject *)PyErr_NoMemory();
	}
	op = PyObject_GC_NewVar(PyTupleObject, &PyTuple_Type, size);
	if (op == NULL)
	return NULL;
	}
	return op;
	}

	static int
	tuple_create_empty_tuple_singleton(struct _Py_tuple_state *state)
	{
	#if PyTuple_MAXSAVESIZE > 0
	assert(state->free_list[0] == NULL);

	PyTupleObject *op = PyObject_GC_NewVar(PyTupleObject, &PyTuple_Type, 0);
	if (op == NULL) {
	return -1;
	}
	// The empty tuple singleton is not tracked by the GC.
	// It does not contain any Python object.

	state->free_list[0] = op;
	state->numfree[0]++;

	assert(state->numfree[0] == 1);
	#endif
	return 0;
	}


	static PyObject *
	tuple_get_empty(void)
	{
	#if PyTuple_MAXSAVESIZE > 0
	struct _Py_tuple_state *state = get_tuple_state();
	PyTupleObject *op = state->free_list[0];
	// tuple_get_empty() must not be called before _PyTuple_Init()
	// or after _PyTuple_Fini()
	assert(op != NULL);
	#ifdef Py_DEBUG
	assert(state->numfree[0] != -1);
	#endif

	Py_INCREF(op);
	return (PyObject *) op;
	#else
	return PyTuple_New(0);
	#endif
	}


	PyObject *
	PyTuple_New(Py_ssize_t size)
	{
	PyTupleObject *op;
	#if PyTuple_MAXSAVESIZE > 0
	if (size == 0) {
	return tuple_get_empty();
	}
	#endif
	op = tuple_alloc(size);
	if (op == NULL) {
	return NULL;
	}
	for (Py_ssize_t i = 0; i < size; i++) {
	op->ob_item[i] = NULL;
	}
	tuple_gc_track(op);
	return (PyObject *) op;
	}

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

	PyObject *
	PyTuple_GetItem(PyObject *op, Py_ssize_t i)
	{
	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];
	}

	int
	PyTuple_SetItem(PyObject op, Py_ssize_t i, PyObject newitem)
	{
	PyObject **p;
	if (!PyTuple_Check(op) \|\| Py_REFCNT(op) != 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;
	Py_XSETREF(*p, newitem);
	return 0;
	}

	void
	_PyTuple_MaybeUntrack(PyObject *op)
	{
	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;
	}
	_PyObject_GC_UNTRACK(op);
	}

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

	if (n == 0) {
	return tuple_get_empty();
	}

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


	/* Methods */

	static void
	tupledealloc(PyTupleObject *op)
	{
	Py_ssize_t len = Py_SIZE(op);
	PyObject_GC_UnTrack(op);
	Py_TRASHCAN_BEGIN(op, tupledealloc)
	if (len > 0) {
	Py_ssize_t i = len;
	while (--i >= 0) {
	Py_XDECREF(op->ob_item[i]);
	}
	#if PyTuple_MAXSAVESIZE > 0
	struct _Py_tuple_state *state = get_tuple_state();
	#ifdef Py_DEBUG
	// tupledealloc() must not be called after _PyTuple_Fini()
	assert(state->numfree[0] != -1);
	#endif
	if (len < PyTuple_MAXSAVESIZE
	&& state->numfree[len] < PyTuple_MAXFREELIST
	&& Py_IS_TYPE(op, &PyTuple_Type))
	{
	op->ob_item[0] = (PyObject *) state->free_list[len];
	state->numfree[len]++;
	state->free_list[len] = op;
	goto done; /* return */
	}
	#endif
	}
	Py_TYPE(op)->tp_free((PyObject *)op);

	#if PyTuple_MAXSAVESIZE > 0
	done:
	#endif
	Py_TRASHCAN_END
	}

	static PyObject *
	tuplerepr(PyTupleObject *v)
	{
	Py_ssize_t i, n;
	_PyUnicodeWriter writer;

	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;
	}

	_PyUnicodeWriter_Init(&writer);
	writer.overallocate = 1;
	if (Py_SIZE(v) > 1) {
	/* "(" + "1" + ", 2" * (len - 1) + ")" */
	writer.min_length = 1 + 1 + (2 + 1) * (Py_SIZE(v) - 1) + 1;
	}
	else {
	/* "(1,)" */
	writer.min_length = 4;
	}

	if (_PyUnicodeWriter_WriteChar(&writer, '(') < 0)
	goto error;

	/* Do repr() on each element. */
	for (i = 0; i < n; ++i) {
	PyObject *s;

	if (i > 0) {
	if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ", 2) < 0)
	goto error;
	}

	s = PyObject_Repr(v->ob_item[i]);
	if (s == NULL)
	goto error;

	if (_PyUnicodeWriter_WriteStr(&writer, s) < 0) {
	Py_DECREF(s);
	goto error;
	}
	Py_DECREF(s);
	}

	writer.overallocate = 0;
	if (n > 1) {
	if (_PyUnicodeWriter_WriteChar(&writer, ')') < 0)
	goto error;
	}
	else {
	if (_PyUnicodeWriter_WriteASCIIString(&writer, ",)", 2) < 0)
	goto error;
	}

	Py_ReprLeave((PyObject *)v);
	return _PyUnicodeWriter_Finish(&writer);

	error:
	_PyUnicodeWriter_Dealloc(&writer);
	Py_ReprLeave((PyObject *)v);
	return NULL;
	}


	/* Hash for tuples. This is a slightly simplified version of the xxHash
	non-cryptographic hash:
	- we do not use any parallellism, there is only 1 accumulator.
	- we drop the final mixing since this is just a permutation of the
	output space: it does not help against collisions.
	- at the end, we mangle the length with a single constant.
	For the xxHash specification, see
	https://github.com/Cyan4973/xxHash/blob/master/doc/xxhash_spec.md

	Below are the official constants from the xxHash specification. Optimizing
	compilers should emit a single "rotate" instruction for the
	_PyHASH_XXROTATE() expansion. If that doesn't happen for some important
	platform, the macro could be changed to expand to a platform-specific rotate
	spelling instead.
	*/
	#if SIZEOF_PY_UHASH_T > 4
	#define _PyHASH_XXPRIME_1 ((Py_uhash_t)11400714785074694791ULL)
	#define _PyHASH_XXPRIME_2 ((Py_uhash_t)14029467366897019727ULL)
	#define _PyHASH_XXPRIME_5 ((Py_uhash_t)2870177450012600261ULL)
	#define _PyHASH_XXROTATE(x) ((x << 31) \| (x >> 33)) /* Rotate left 31 bits */
	#else
	#define _PyHASH_XXPRIME_1 ((Py_uhash_t)2654435761UL)
	#define _PyHASH_XXPRIME_2 ((Py_uhash_t)2246822519UL)
	#define _PyHASH_XXPRIME_5 ((Py_uhash_t)374761393UL)
	#define _PyHASH_XXROTATE(x) ((x << 13) \| (x >> 19)) /* Rotate left 13 bits */
	#endif

	/* Tests have shown that it's not worth to cache the hash value, see
	https://bugs.python.org/issue9685 */
	static Py_hash_t
	tuplehash(PyTupleObject *v)
	{
	Py_ssize_t i, len = Py_SIZE(v);
	PyObject **item = v->ob_item;

	Py_uhash_t acc = _PyHASH_XXPRIME_5;
	for (i = 0; i < len; i++) {
	Py_uhash_t lane = PyObject_Hash(item[i]);
	if (lane == (Py_uhash_t)-1) {
	return -1;
	}
	acc += lane * _PyHASH_XXPRIME_2;
	acc = _PyHASH_XXROTATE(acc);
	acc *= _PyHASH_XXPRIME_1;
	}

	/* Add input length, mangled to keep the historical value of hash(()). */
	acc += len ^ (_PyHASH_XXPRIME_5 ^ 3527539UL);

	if (acc == (Py_uhash_t)-1) {
	return 1546275796;
	}
	return acc;
	}

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

	static int
	tuplecontains(PyTupleObject a, PyObject el)
	{
	Py_ssize_t i;
	int cmp;

	for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i)
	cmp = PyObject_RichCompareBool(PyTuple_GET_ITEM(a, i), el, Py_EQ);
	return cmp;
	}

	static PyObject *
	tupleitem(PyTupleObject *a, Py_ssize_t i)
	{
	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];
	}

	PyObject *
	_PyTuple_FromArray(PyObject const src, Py_ssize_t n)
	{
	if (n == 0) {
	return tuple_get_empty();
	}

	PyTupleObject *tuple = tuple_alloc(n);
	if (tuple == NULL) {
	return NULL;
	}
	PyObject **dst = tuple->ob_item;
	for (Py_ssize_t i = 0; i < n; i++) {
	PyObject *item = src[i];
	Py_INCREF(item);
	dst[i] = item;
	}
	tuple_gc_track(tuple);
	return (PyObject *)tuple;
	}

	static PyObject *
	tupleslice(PyTupleObject *a, Py_ssize_t ilow,
	Py_ssize_t ihigh)
	{
	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;
	}
	return _PyTuple_FromArray(a->ob_item + ilow, ihigh - ilow);
	}

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

	static PyObject *
	tupleconcat(PyTupleObject a, PyObject bb)
	{
	Py_ssize_t size;
	Py_ssize_t i;
	PyObject src, dest;
	PyTupleObject *np;
	if (Py_SIZE(a) == 0 && PyTuple_CheckExact(bb)) {
	Py_INCREF(bb);
	return bb;
	}
	if (!PyTuple_Check(bb)) {
	PyErr_Format(PyExc_TypeError,
	"can only concatenate tuple (not \"%.200s\") to tuple",
	Py_TYPE(bb)->tp_name);
	return NULL;
	}
	PyTupleObject b = (PyTupleObject )bb;

	if (Py_SIZE(b) == 0 && PyTuple_CheckExact(a)) {
	Py_INCREF(a);
	return (PyObject *)a;
	}
	assert((size_t)Py_SIZE(a) + (size_t)Py_SIZE(b) < PY_SSIZE_T_MAX);
	size = Py_SIZE(a) + Py_SIZE(b);
	if (size == 0) {
	return tuple_get_empty();
	}

	np = tuple_alloc(size);
	if (np == NULL) {
	return NULL;
	}
	src = /old?u=https%3A%2F%2Fgithub.com%2Fpython%2Fcpython%2Fblob%2Fmaster%2FObjects%2Fa-%26gt%3B%3Cspan&y=1999 class="pl-smi">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 = /old?u=https%3A%2F%2Fgithub.com%2Fpython%2Fcpython%2Fblob%2Fmaster%2FObjects%2Fb-%26gt%3B%3Cspan&y=1999 class="pl-smi">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;
	}
	tuple_gc_track(np);
	return (PyObject *)np;
	}

	static PyObject *
	tuplerepeat(PyTupleObject *a, Py_ssize_t n)
	{
	Py_ssize_t i, j;
	Py_ssize_t size;
	PyTupleObject *np;
	PyObject p, items;
	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 \|\| n <= 0) {
	return tuple_get_empty();
	}
	if (n > PY_SSIZE_T_MAX / Py_SIZE(a))
	return PyErr_NoMemory();
	size = Py_SIZE(a) * n;
	np = tuple_alloc(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++;
	}
	}
	tuple_gc_track(np);
	return (PyObject *) np;
	}

	/*[clinic input]
	tuple.index

	value: object
	start: slice_index(accept={int}) = 0
	stop: slice_index(accept={int}, c_default="PY_SSIZE_T_MAX") = sys.maxsize
	/

	Return first index of value.

	Raises ValueError if the value is not present.
	[clinic start generated code]*/

	static PyObject *
	tuple_index_impl(PyTupleObject self, PyObject value, Py_ssize_t start,
	Py_ssize_t stop)
	/[clinic end generated code: output=07b6f9f3cb5c33eb input=fb39e9874a21fe3f]/
	{
	Py_ssize_t i;

	if (start < 0) {
	start += Py_SIZE(self);
	if (start < 0)
	start = 0;
	}
	if (stop < 0) {
	stop += Py_SIZE(self);
	}
	else if (stop > Py_SIZE(self)) {
	stop = Py_SIZE(self);
	}
	for (i = start; i < stop; i++) {
	int cmp = PyObject_RichCompareBool(self->ob_item[i], value, 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;
	}

	/*[clinic input]
	tuple.count

	value: object
	/

	Return number of occurrences of value.
	[clinic start generated code]*/

	static PyObject *
	tuple_count(PyTupleObject self, PyObject value)
	/[clinic end generated code: output=aa927affc5a97605 input=531721aff65bd772]/
	{
	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], value, Py_EQ);
	if (cmp > 0)
	count++;
	else if (cmp < 0)
	return NULL;
	}
	return PyLong_FromSsize_t(count);
	}

	static int
	tupletraverse(PyTupleObject o, visitproc visit, void arg)
	{
	Py_ssize_t i;

	for (i = Py_SIZE(o); --i >= 0; )
	Py_VISIT(o->ob_item[i]);
	return 0;
	}

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

	if (!PyTuple_Check(v) \|\| !PyTuple_Check(w))
	Py_RETURN_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 */
	Py_RETURN_RICHCOMPARE(vlen, wlen, op);
	}

	/* We have an item that differs -- shortcuts for EQ/NE */
	if (op == Py_EQ) {
	Py_RETURN_FALSE;
	}
	if (op == Py_NE) {
	Py_RETURN_TRUE;
	}

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

	static PyObject *
	tuple_subtype_new(PyTypeObject type, PyObject iterable);

	/*[clinic input]
	@classmethod
	tuple.__new__ as tuple_new
	iterable: object(c_default="NULL") = ()
	/

	Built-in immutable sequence.

	If no argument is given, the constructor returns an empty tuple.
	If iterable is specified the tuple is initialized from iterable's items.

	If the argument is a tuple, the return value is the same object.
	[clinic start generated code]*/

	static PyObject *
	tuple_new_impl(PyTypeObject type, PyObject iterable)
	/[clinic end generated code: output=4546d9f0d469bce7 input=86963bcde633b5a2]/
	{
	if (type != &PyTuple_Type)
	return tuple_subtype_new(type, iterable);

	if (iterable == NULL) {
	return tuple_get_empty();
	}
	else {
	return PySequence_Tuple(iterable);
	}
	}

	static PyObject *
	tuple_vectorcall(PyObject type, PyObject const*args,
	size_t nargsf, PyObject *kwnames)
	{
	if (!_PyArg_NoKwnames("tuple", kwnames)) {
	return NULL;
	}

	Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
	if (!_PyArg_CheckPositional("tuple", nargs, 0, 1)) {
	return NULL;
	}

	if (nargs) {
	return tuple_new_impl((PyTypeObject *)type, args[0]);
	}
	else {
	return tuple_get_empty();
	}
	}

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

	assert(PyType_IsSubtype(type, &PyTuple_Type));
	tmp = tuple_new_impl(&PyTuple_Type, iterable);
	if (tmp == NULL)
	return NULL;
	assert(PyTuple_Check(tmp));
	newobj = type->tp_alloc(type, n = PyTuple_GET_SIZE(tmp));
	if (newobj == NULL) {
	Py_DECREF(tmp);
	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;
	}

	static PySequenceMethods tuple_as_sequence = {
	(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 */
	};

	static PyObject*
	tuplesubscript(PyTupleObject* self, PyObject* item)
	{
	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, i;
	size_t cur;
	PyObject* it;
	PyObject src, dest;

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

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

	src = /old?u=https%3A%2F%2Fgithub.com%2Fpython%2Fcpython%2Fblob%2Fmaster%2FObjects%2Fself-%26gt%3B%3Cspan&y=1999 class="pl-smi">ob_item;
	dest = result->ob_item;
	for (cur = start, i = 0; i < slicelength;
	cur += step, i++) {
	it = src[cur];
	Py_INCREF(it);
	dest[i] = it;
	}

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

	/*[clinic input]
	tuple.__getnewargs__
	[clinic start generated code]*/

	static PyObject *
	tuple___getnewargs___impl(PyTupleObject *self)
	/[clinic end generated code: output=25e06e3ee56027e2 input=1aeb4b286a21639a]/
	{
	return Py_BuildValue("(N)", tupleslice(self, 0, Py_SIZE(self)));
	}

	static PyMethodDef tuple_methods[] = {
	TUPLE___GETNEWARGS___METHODDEF
	TUPLE_INDEX_METHODDEF
	TUPLE_COUNT_METHODDEF
	{"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O\|METH_CLASS, PyDoc_STR("See PEP 585")},
	{NULL, NULL} /* sentinel */
	};

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

	static PyObject tuple_iter(PyObject seq);

	PyTypeObject PyTuple_Type = {
	PyVarObject_HEAD_INIT(&PyType_Type, 0)
	"tuple",
	sizeof(PyTupleObject) - sizeof(PyObject *),
	sizeof(PyObject *),
	(destructor)tupledealloc, /* tp_dealloc */
	0, /* tp_vectorcall_offset */
	0, /* tp_getattr */
	0, /* tp_setattr */
	0, /* tp_as_async */
	(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_new__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 */
	.tp_vectorcall = tuple_vectorcall,
	};

	/* 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
	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
	known to some other part of the code. */

	int
	_PyTuple_Resize(PyObject **pv, Py_ssize_t newsize)
	{
	PyTupleObject *v;
	PyTupleObject *sv;
	Py_ssize_t i;
	Py_ssize_t oldsize;

	v = (PyTupleObject ) pv;
	if (v == NULL \|\| !Py_IS_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 */
	#ifdef Py_REF_DEBUG
	_Py_RefTotal--;
	#endif
	if (_PyObject_GC_IS_TRACKED(v)) {
	_PyObject_GC_UNTRACK(v);
	}
	#ifdef Py_TRACE_REFS
	_Py_ForgetReference((PyObject *) v);
	#endif
	/* DECREF items deleted by shrinkage */
	for (i = newsize; i < oldsize; i++) {
	Py_CLEAR(v->ob_item[i]);
	}
	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;
	}

	void
	_PyTuple_ClearFreeList(PyThreadState *tstate)
	{
	#if PyTuple_MAXSAVESIZE > 0
	struct _Py_tuple_state *state = &tstate->interp->tuple;
	for (Py_ssize_t i = 1; i < PyTuple_MAXSAVESIZE; i++) {
	PyTupleObject *p = state->free_list[i];
	state->free_list[i] = NULL;
	state->numfree[i] = 0;
	while (p) {
	PyTupleObject *q = p;
	p = (PyTupleObject *)(p->ob_item[0]);
	PyObject_GC_Del(q);
	}
	}
	// the empty tuple singleton is only cleared by _PyTuple_Fini()
	#endif
	}


	PyStatus
	_PyTuple_Init(PyThreadState *tstate)
	{
	struct _Py_tuple_state *state = &tstate->interp->tuple;
	if (tuple_create_empty_tuple_singleton(state) < 0) {
	return _PyStatus_NO_MEMORY();
	}
	return _PyStatus_OK();
	}


	void
	_PyTuple_Fini(PyThreadState *tstate)
	{
	#if PyTuple_MAXSAVESIZE > 0
	struct _Py_tuple_state *state = &tstate->interp->tuple;
	// The empty tuple singleton must not be tracked by the GC
	assert(!_PyObject_GC_IS_TRACKED(state->free_list[0]));
	Py_CLEAR(state->free_list[0]);
	_PyTuple_ClearFreeList(tstate);
	#ifdef Py_DEBUG
	state->numfree[0] = -1;
	#endif
	#endif
	}

	/********************* Tuple Iterator ************************/

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

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

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

	static PyObject *
	tupleiter_next(tupleiterobject *it)
	{
	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;
	}

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

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

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

	static PyObject *
	tupleiter_reduce(tupleiterobject it, PyObject Py_UNUSED(ignored))
	{
	_Py_IDENTIFIER(iter);
	if (it->it_seq)
	return Py_BuildValue("N(O)n", _PyEval_GetBuiltinId(&PyId_iter),
	it->it_seq, it->it_index);
	else
	return Py_BuildValue("N(())", _PyEval_GetBuiltinId(&PyId_iter));
	}

	static PyObject *
	tupleiter_setstate(tupleiterobject it, PyObject state)
	{
	Py_ssize_t index = PyLong_AsSsize_t(state);
	if (index == -1 && PyErr_Occurred())
	return NULL;
	if (it->it_seq != NULL) {
	if (index < 0)
	index = 0;
	else if (index > PyTuple_GET_SIZE(it->it_seq))
	index = PyTuple_GET_SIZE(it->it_seq); /* exhausted iterator */
	it->it_index = index;
	}
	Py_RETURN_NONE;
	}

	PyDoc_STRVAR(reduce_doc, "Return state information for pickling.");
	PyDoc_STRVAR(setstate_doc, "Set state information for unpickling.");

	static PyMethodDef tupleiter_methods[] = {
	{"__length_hint__", (PyCFunction)tupleiter_len, METH_NOARGS, length_hint_doc},
	{"__reduce__", (PyCFunction)tupleiter_reduce, METH_NOARGS, reduce_doc},
	{"__setstate__", (PyCFunction)tupleiter_setstate, METH_O, setstate_doc},
	{NULL, NULL} /* sentinel */
	};

	PyTypeObject PyTupleIter_Type = {
	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_vectorcall_offset */
	0, /* tp_getattr */
	0, /* tp_setattr */
	0, /* tp_as_async */
	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,
	};

	static PyObject *
	tuple_iter(PyObject *seq)
	{
	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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