/* set object implementation

Written and maintained by Raymond D. Hettinger <[email protected]>

Derived from Lib/sets.py and Objects/dictobject.c.

Copyright (c) 2003-6 Python Software Foundation.

All rights reserved.

*/

#include "Python.h"

#include "structmember.h"

/* This must be >= 1. */

#define PERTURB_SHIFT 5

/* Object used as dummy key to fill deleted entries */

static PyObject *dummy = NULL; /* Initialized by first call to make_new_set() */

#ifdef Py_REF_DEBUG

PyObject *

_PySet_Dummy(void)

{

return dummy;

}

#endif

#define INIT_NONZERO_SET_SLOTS(so) do { \

(so)->table = (so)->smalltable; \

(so)->mask = PySet_MINSIZE - 1; \

(so)->hash = -1; \

} while(0)

#define EMPTY_TO_MINSIZE(so) do { \

memset((so)->smalltable, 0, sizeof((so)->smalltable)); \

(so)->used = (so)->fill = 0; \

INIT_NONZERO_SET_SLOTS(so); \

} while(0)

/* Reuse scheme to save calls to malloc, free, and memset */

#define MAXFREESETS 80

static PySetObject *free_sets[MAXFREESETS];

static int num_free_sets = 0;

/*

The basic lookup function used by all operations.

This is based on Algorithm D from Knuth Vol. 3, Sec. 6.4.

Open addressing is preferred over chaining since the link overhead for

chaining would be substantial (100% with typical malloc overhead).

The initial probe index is computed as hash mod the table size. Subsequent

probe indices are computed as explained in Objects/dictobject.c.

All arithmetic on hash should ignore overflow.

Unlike the dictionary implementation, the lookkey functions can return

NULL if the rich comparison returns an error.

*/

static setentry *

set_lookkey(PySetObject *so, PyObject *key, register long hash)

{

register Py_ssize_t i;

register size_t perturb;

register setentry *freeslot;

register size_t mask = so->mask;

setentry *table = so->table;

register setentry *entry;

register int cmp;

PyObject *startkey;

i = hash & mask;

entry = &table[i];

if (entry->key == NULL || entry->key == key)

return entry;

if (entry->key == dummy)

freeslot = entry;

else {

if (entry->hash == hash) {

startkey = entry->key;

cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);

if (cmp < 0)

return NULL;

if (table == so->table && entry->key == startkey) {

if (cmp > 0)

return entry;

}

else {

/* The compare did major nasty stuff to the

* set: start over.

*/

return set_lookkey(so, key, hash);

}

}

freeslot = NULL;

}

/* In the loop, key == dummy is by far (factor of 100s) the

least likely outcome, so test for that last. */

for (perturb = hash; ; perturb >>= PERTURB_SHIFT) {

i = (i << 2) + i + perturb + 1;

entry = &table[i & mask];

if (entry->key == NULL) {

if (freeslot != NULL)

entry = freeslot;

break;

}

if (entry->key == key)

break;

if (entry->hash == hash && entry->key != dummy) {

startkey = entry->key;

cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);

if (cmp < 0)

return NULL;

if (table == so->table && entry->key == startkey) {

if (cmp > 0)

break;

}

else {

/* The compare did major nasty stuff to the

* set: start over.

*/

return set_lookkey(so, key, hash);

}

}

else if (entry->key == dummy && freeslot == NULL)

freeslot = entry;

}

return entry;

}

/*

* Hacked up version of set_lookkey which can assume keys are always strings;

* This means we can always use _PyString_Eq directly and not have to check to

* see if the comparison altered the table.

*/

static setentry *

set_lookkey_string(PySetObject *so, PyObject *key, register long hash)

{

register Py_ssize_t i;

register size_t perturb;

register setentry *freeslot;

register size_t mask = so->mask;

setentry *table = so->table;

register setentry *entry;

/* Make sure this function doesn't have to handle non-string keys,

including subclasses of str; e.g., one reason to subclass

strings is to override __eq__, and for speed we don't cater to

that here. */

if (!PyString_CheckExact(key)) {

so->lookup = set_lookkey;

return set_lookkey(so, key, hash);

}

i = hash & mask;

entry = &table[i];

if (entry->key == NULL || entry->key == key)

return entry;

if (entry->key == dummy)

freeslot = entry;

else {

if (entry->hash == hash && _PyString_Eq(entry->key, key))

return entry;

freeslot = NULL;

}

/* In the loop, key == dummy is by far (factor of 100s) the

least likely outcome, so test for that last. */

for (perturb = hash; ; perturb >>= PERTURB_SHIFT) {

i = (i << 2) + i + perturb + 1;

entry = &table[i & mask];

if (entry->key == NULL)

return freeslot == NULL ? entry : freeslot;

if (entry->key == key

|| (entry->hash == hash

&& entry->key != dummy

&& _PyString_Eq(entry->key, key)))

return entry;

if (entry->key == dummy && freeslot == NULL)

freeslot = entry;

}

}

/*

Internal routine to insert a new key into the table.

Used both by the internal resize routine and by the public insert routine.

Eats a reference to key.

*/

static int

set_insert_key(register PySetObject *so, PyObject *key, long hash)

{

register setentry *entry;

typedef setentry *(*lookupfunc)(PySetObject *, PyObject *, long);

assert(so->lookup != NULL);

entry = so->lookup(so, key, hash);

if (entry == NULL)

return -1;

if (entry->key == NULL) {

/* UNUSED */

so->fill++;

entry->key = key;

entry->hash = hash;

so->used++;

} else if (entry->key == dummy) {

/* DUMMY */

entry->key = key;

entry->hash = hash;

so->used++;

Py_DECREF(dummy);

} else {

/* ACTIVE */

Py_DECREF(key);

}

return 0;

}

/*

Restructure the table by allocating a new table and reinserting all

keys again. When entries have been deleted, the new table may

actually be smaller than the old one.

*/

static int

set_table_resize(PySetObject *so, Py_ssize_t minused)

{

Py_ssize_t newsize;

setentry *oldtable, *newtable, *entry;

Py_ssize_t i;

int is_oldtable_malloced;

setentry small_copy[PySet_MINSIZE];

assert(minused >= 0);

/* Find the smallest table size > minused. */

for (newsize = PySet_MINSIZE;

newsize <= minused && newsize > 0;

newsize <<= 1)

;

if (newsize <= 0) {

PyErr_NoMemory();

return -1;

}

/* Get space for a new table. */

oldtable = so->table;

assert(oldtable != NULL);

is_oldtable_malloced = oldtable != so->smalltable;

if (newsize == PySet_MINSIZE) {

/* A large table is shrinking, or we can't get any smaller. */

newtable = so->smalltable;

if (newtable == oldtable) {

if (so->fill == so->used) {

/* No dummies, so no point doing anything. */

return 0;

}

/* We're not going to resize it, but rebuild the

table anyway to purge old dummy entries.

Subtle: This is *necessary* if fill==size,

as set_lookkey needs at least one virgin slot to

terminate failing searches. If fill < size, it's

merely desirable, as dummies slow searches. */

assert(so->fill > so->used);

memcpy(small_copy, oldtable, sizeof(small_copy));

oldtable = small_copy;

}

}

else {

newtable = PyMem_NEW(setentry, newsize);

if (newtable == NULL) {

PyErr_NoMemory();

return -1;

}

}

/* Make the set empty, using the new table. */

assert(newtable != oldtable);

so->table = newtable;

so->mask = newsize - 1;

memset(newtable, 0, sizeof(setentry) * newsize);

so->used = 0;

i = so->fill;

so->fill = 0;

/* Copy the data over; this is refcount-neutral for active entries;

dummy entries aren't copied over, of course */

for (entry = oldtable; i > 0; entry++) {

if (entry->key == NULL) {

/* UNUSED */

;

} else if (entry->key == dummy) {

/* DUMMY */

--i;

assert(entry->key == dummy);

Py_DECREF(entry->key);

} else {

/* ACTIVE */

--i;

if(set_insert_key(so, entry->key, entry->hash) == -1) {

if (is_oldtable_malloced)

PyMem_DEL(oldtable);

return -1;

}

}

}

if (is_oldtable_malloced)

PyMem_DEL(oldtable);

return 0;

}

/* CAUTION: set_add_key/entry() must guarantee it won't resize the table */

static int

set_add_entry(register PySetObject *so, setentry *entry)

{

register Py_ssize_t n_used;

assert(so->fill <= so->mask); /* at least one empty slot */

n_used = so->used;

Py_INCREF(entry->key);

if (set_insert_key(so, entry->key, entry->hash) == -1)

return -1;

if (!(so->used > n_used && so->fill*3 >= (so->mask+1)*2))

return 0;

return set_table_resize(so, so->used>50000 ? so->used*2 : so->used*4);

}

static int

set_add_key(register PySetObject *so, PyObject *key)

{

register long hash;

register Py_ssize_t n_used;

if (!PyString_CheckExact(key) ||

(hash = ((PyStringObject *) key)->ob_shash) == -1) {

hash = PyObject_Hash(key);

if (hash == -1)

return -1;

}

assert(so->fill <= so->mask); /* at least one empty slot */

n_used = so->used;

Py_INCREF(key);

if (set_insert_key(so, key, hash) == -1) {

Py_DECREF(key);

return -1;

}

if (!(so->used > n_used && so->fill*3 >= (so->mask+1)*2))

return 0;

return set_table_resize(so, so->used>50000 ? so->used*2 : so->used*4);

}

#define DISCARD_NOTFOUND 0

#define DISCARD_FOUND 1

static int

set_discard_entry(PySetObject *so, setentry *oldentry)

{ register setentry *entry;

PyObject *old_key;

entry = (so->lookup)(so, oldentry->key, oldentry->hash);

if (entry == NULL)

return -1;

if (entry->key == NULL || entry->key == dummy)

return DISCARD_NOTFOUND;

old_key = entry->key;

Py_INCREF(dummy);

entry->key = dummy;

so->used--;

Py_DECREF(old_key);

return DISCARD_FOUND;

}

static int

set_discard_key(PySetObject *so, PyObject *key)

{

register long hash;

register setentry *entry;

PyObject *old_key;

assert (PyAnySet_Check(so));

if (!PyString_CheckExact(key) ||

(hash = ((PyStringObject *) key)->ob_shash) == -1) {

hash = PyObject_Hash(key);

if (hash == -1)

return -1;

}

entry = (so->lookup)(so, key, hash);

if (entry == NULL)

return -1;

if (entry->key == NULL || entry->key == dummy)

return DISCARD_NOTFOUND;

old_key = entry->key;

Py_INCREF(dummy);

entry->key = dummy;

so->used--;

Py_DECREF(old_key);

return DISCARD_FOUND;

}

static int

set_clear_internal(PySetObject *so)

{

setentry *entry, *table;

int table_is_malloced;

Py_ssize_t fill;

setentry small_copy[PySet_MINSIZE];

#ifdef Py_DEBUG

Py_ssize_t i, n;

assert (PyAnySet_Check(so));

n = so->mask + 1;

i = 0;

#endif

table = so->table;

assert(table != NULL);

table_is_malloced = table != so->smalltable;

/* This is delicate. During the process of clearing the set,

* decrefs can cause the set to mutate. To avoid fatal confusion

* (voice of experience), we have to make the set empty before

* clearing the slots, and never refer to anything via so->ref while

* clearing.

*/

fill = so->fill;

if (table_is_malloced)

EMPTY_TO_MINSIZE(so);

else if (fill > 0) {

/* It's a small table with something that needs to be cleared.

* Afraid the only safe way is to copy the set entries into

* another small table first.

*/

memcpy(small_copy, table, sizeof(small_copy));

table = small_copy;

EMPTY_TO_MINSIZE(so);

}

/* else it's a small table that's already empty */

/* Now we can finally clear things. If C had refcounts, we could

* assert that the refcount on table is 1 now, i.e. that this function

* has unique access to it, so decref side-effects can't alter it.

*/

for (entry = table; fill > 0; ++entry) {

#ifdef Py_DEBUG

assert(i < n);

++i;

#endif

if (entry->key) {

--fill;

Py_DECREF(entry->key);

}

#ifdef Py_DEBUG

else

assert(entry->key == NULL);

#endif

}

if (table_is_malloced)

PyMem_DEL(table);

return 0;

}

/*

* Iterate over a set table. Use like so:

*

* Py_ssize_t pos;

* setentry *entry;

* pos = 0; # important! pos should not otherwise be changed by you

* while (set_next(yourset, &pos, &entry)) {

* Refer to borrowed reference in entry->key.

* }

*

* CAUTION: In general, it isn't safe to use set_next in a loop that

* mutates the table.

*/

static int

set_next(PySetObject *so, Py_ssize_t *pos_ptr, setentry **entry_ptr)

{

Py_ssize_t i;

Py_ssize_t mask;

register setentry *table;

assert (PyAnySet_Check(so));

i = *pos_ptr;

assert(i >= 0);

table = so->table;

mask = so->mask;

while (i <= mask && (table[i].key == NULL || table[i].key == dummy))

i++;

*pos_ptr = i+1;

if (i > mask)

return 0;

assert(table[i].key != NULL);

*entry_ptr = &table[i];

return 1;

}

static void

set_dealloc(PySetObject *so)

{

register setentry *entry;

Py_ssize_t fill = so->fill;

PyObject_GC_UnTrack(so);

Py_TRASHCAN_SAFE_BEGIN(so)

if (so->weakreflist != NULL)

PyObject_ClearWeakRefs((PyObject *) so);

for (entry = so->table; fill > 0; entry++) {

if (entry->key) {

--fill;

Py_DECREF(entry->key);

}

}

if (so->table != so->smalltable)

PyMem_DEL(so->table);

if (num_free_sets < MAXFREESETS && PyAnySet_CheckExact(so))

free_sets[num_free_sets++] = so;

else

so->ob_type->tp_free(so);

Py_TRASHCAN_SAFE_END(so)

}

static int

set_tp_print(PySetObject *so, FILE *fp, int flags)

{

setentry *entry;

Py_ssize_t pos=0;

char *emit = ""; /* No separator emitted on first pass */

char *separator = ", ";

int literalform = 0;

if (!so->used) {

fprintf(fp, "%s()", so->ob_type->tp_name);

return 0;

}

if (so->ob_type == &PySet_Type) {

literalform = 1;

fprintf(fp, "{");

} else

fprintf(fp, "%s([", so->ob_type->tp_name);

while (set_next(so, &pos, &entry)) {

fputs(emit, fp);

emit = separator;

if (PyObject_Print(entry->key, fp, 0) != 0)

return -1;

}

if (literalform)

fputs("}", fp);

else

fputs("])", fp);

return 0;

}

static PyObject *

set_repr(PySetObject *so)

{

PyObject *keys, *result, *listrepr;

/* shortcut for the empty set */

if (!so->used)

return PyString_FromFormat("%s()", so->ob_type->tp_name);

keys = PySequence_List((PyObject *)so);

if (keys == NULL)

return NULL;

listrepr = PyObject_Repr(keys);

Py_DECREF(keys);

if (listrepr == NULL)

return NULL;

if (so->ob_type == &PySet_Type) {

char *s = PyString_AS_STRING(listrepr);

s += 1;

s[strlen(s)-1] = 0;

result = PyString_FromFormat("{%s}", s);

} else {

result = PyString_FromFormat("%s(%s)", so->ob_type->tp_name,

PyString_AS_STRING(listrepr));

}

Py_DECREF(listrepr);

return result;

}

static Py_ssize_t

set_len(PyObject *so)

{

return ((PySetObject *)so)->used;

}

static int

set_merge(PySetObject *so, PyObject *otherset)

{

PySetObject *other;

register Py_ssize_t i;

register setentry *entry;

assert (PyAnySet_Check(so));

assert (PyAnySet_Check(otherset));

other = (PySetObject*)otherset;

if (other == so || other->used == 0)

/* a.update(a) or a.update({}); nothing to do */

return 0;

/* Do one big resize at the start, rather than

* incrementally resizing as we insert new keys. Expect

* that there will be no (or few) overlapping keys.

*/

if ((so->fill + other->used)*3 >= (so->mask+1)*2) {

if (set_table_resize(so, (so->used + other->used)*2) != 0)

return -1;

}

for (i = 0; i <= other->mask; i++) {

entry = &other->table[i];

if (entry->key != NULL &&

entry->key != dummy) {

Py_INCREF(entry->key);

if (set_insert_key(so, entry->key, entry->hash) == -1) {

Py_DECREF(entry->key);

return -1;

}

}

}

return 0;

}

static int

set_contains_key(PySetObject *so, PyObject *key)

{

long hash;

setentry *entry;

if (!PyString_CheckExact(key) ||

(hash = ((PyStringObject *) key)->ob_shash) == -1) {

hash = PyObject_Hash(key);

if (hash == -1)

return -1;

}

entry = (so->lookup)(so, key, hash);

if (entry == NULL)

return -1;

key = entry->key;

return key != NULL && key != dummy;

}

static int

set_contains_entry(PySetObject *so, setentry *entry)

{

PyObject *key;

setentry *lu_entry;

lu_entry = (so->lookup)(so, entry->key, entry->hash);

if (lu_entry == NULL)

return -1;

key = lu_entry->key;

return key != NULL && key != dummy;

}

static PyObject *

set_pop(PySetObject *so)

{

register Py_ssize_t i = 0;

register setentry *entry;

PyObject *key;

assert (PyAnySet_Check(so));

if (so->used == 0) {

PyErr_SetString(PyExc_KeyError, "pop from an empty set");

return NULL;

}

/* Set entry to "the first" unused or dummy set entry. We abuse

* the hash field of slot 0 to hold a search finger:

* If slot 0 has a value, use slot 0.

* Else slot 0 is being used to hold a search finger,

* and we use its hash value as the first index to look.

*/

entry = &so->table[0];

if (entry->key == NULL || entry->key == dummy) {

i = entry->hash;

/* The hash field may be a real hash value, or it may be a

* legit search finger, or it may be a once-legit search

* finger that's out of bounds now because it wrapped around

* or the table shrunk -- simply make sure it's in bounds now.

*/

if (i > so->mask || i < 1)

i = 1; /* skip slot 0 */

while ((entry = &so->table[i])->key == NULL || entry->key==dummy) {

i++;

if (i > so->mask)

i = 1;

}

}

key = entry->key;

Py_INCREF(dummy);

entry->key = dummy;

so->used--;

so->table[0].hash = i + 1; /* next place to start */

return key;

}

PyDoc_STRVAR(pop_doc, "Remove and return an arbitrary set element.");

static int

set_traverse(PySetObject *so, visitproc visit, void *arg)

{

Py_ssize_t pos = 0;

setentry *entry;

while (set_next(so, &pos, &entry))

Py_VISIT(entry->key);

return 0;

}

static long

frozenset_hash(PyObject *self)

{

PySetObject *so = (PySetObject *)self;

long h, hash = 1927868237L;

setentry *entry;

Py_ssize_t pos = 0;

if (so->hash != -1)

return so->hash;

hash *= PySet_GET_SIZE(self) + 1;

while (set_next(so, &pos, &entry)) {

/* Work to increase the bit dispersion for closely spaced hash

values. The is important because some use cases have many

combinations of a small number of elements with nearby

hashes so that many distinct combinations collapse to only

a handful of distinct hash values. */

h = entry->hash;

hash ^= (h ^ (h << 16) ^ 89869747L) * 3644798167u;

}

hash = hash * 69069L + 907133923L;

if (hash == -1)

hash = 590923713L;

so->hash = hash;

return hash;

}

/***** Set iterator type ***********************************************/

typedef struct {

PyObject_HEAD

PySetObject *si_set; /* Set to NULL when iterator is exhausted */

Py_ssize_t si_used;

Py_ssize_t si_pos;

Py_ssize_t len;

} setiterobject;

static void

setiter_dealloc(setiterobject *si)

{

Py_XDECREF(si->si_set);

PyObject_Del(si);

}

static PyObject *

setiter_len(setiterobject *si)

{

Py_ssize_t len = 0;

if (si->si_set != NULL && si->si_used == si->si_set->used)

len = si->len;

return PyInt_FromLong(len);

}

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

static PyMethodDef setiter_methods[] = {

{"__length_hint__", (PyCFunction)setiter_len, METH_NOARGS, length_hint_doc},

{NULL, NULL} /* sentinel */

};

static PyObject *setiter_iternext(setiterobject *si)

{

PyObject *key;

register Py_ssize_t i, mask;

register setentry *entry;

PySetObject *so = si->si_set;

if (so == NULL)

return NULL;

assert (PyAnySet_Check(so));

if (si->si_used != so->used) {

PyErr_SetString(PyExc_RuntimeError,

"Set changed size during iteration");

si->si_used = -1; /* Make this state sticky */

return NULL;

}

i = si->si_pos;

assert(i>=0);

entry = so->table;

mask = so->mask;

while (i <= mask && (entry[i].key == NULL || entry[i].key == dummy))

i++;

si->si_pos = i+1;

if (i > mask)

goto fail;

si->len--;

key = entry[i].key;

Py_INCREF(key);

return key;

fail:

Py_DECREF(so);

si->si_set = NULL;

return NULL;

}

static PyTypeObject PySetIter_Type = {

PyObject_HEAD_INIT(&PyType_Type)

0, /* ob_size */

"setiterator", /* tp_name */

sizeof(setiterobject), /* tp_basicsize */

0, /* tp_itemsize */

/* methods */

(destructor)setiter_dealloc, /* tp_dealloc */

0, /* tp_print */

0, /* tp_getattr */

0, /* tp_setattr */

0, /* tp_compare */

0, /* tp_repr */

0, /* tp_as_number */

0, /* tp_as_sequence */

0, /* tp_as_mapping */

0, /* tp_hash */

0, /* tp_call */

0, /* tp_str */

PyObject_GenericGetAttr, /* tp_getattro */

0, /* tp_setattro */

0, /* tp_as_buffer */

Py_TPFLAGS_DEFAULT, /* tp_flags */

0, /* tp_doc */

0, /* tp_traverse */

0, /* tp_clear */

0, /* tp_richcompare */

0, /* tp_weaklistoffset */

PyObject_SelfIter, /* tp_iter */

(iternextfunc)setiter_iternext, /* tp_iternext */

setiter_methods, /* tp_methods */

0,

};

static PyObject *

set_iter(PySetObject *so)

{

setiterobject *si = PyObject_New(setiterobject, &PySetIter_Type);

if (si == NULL)

return NULL;

Py_INCREF(so);

si->si_set = so;

si->si_used = so->used;

si->si_pos = 0;

si->len = so->used;

return (PyObject *)si;

}

static int

set_update_internal(PySetObject *so, PyObject *other)

{

PyObject *key, *it;

if (PyAnySet_Check(other))

return set_merge(so, other);

if (PyDict_Check(other)) {

PyObject *value;

Py_ssize_t pos = 0;

while (PyDict_Next(other, &pos, &key, &value)) {

if (set_add_key(so, key) == -1)

return -1;

}

return 0;

}

it = PyObject_GetIter(other);

if (it == NULL)

return -1;

while ((key = PyIter_Next(it)) != NULL) {

if (set_add_key(so, key) == -1) {

Py_DECREF(it);

Py_DECREF(key);

return -1;

}

Py_DECREF(key);

}

Py_DECREF(it);

if (PyErr_Occurred())

return -1;

return 0;

}

static PyObject *

set_update(PySetObject *so, PyObject *other)

{

if (set_update_internal(so, other) == -1)

return NULL;

Py_RETURN_NONE;

}

PyDoc_STRVAR(update_doc,

"Update a set with the union of itself and another.");

static PyObject *

make_new_set(PyTypeObject *type, PyObject *iterable)

{

register PySetObject *so = NULL;

if (dummy == NULL) { /* Auto-initialize dummy */

dummy = PyString_FromString("<dummy key>");

if (dummy == NULL)

return NULL;

}

/* create PySetObject structure */

if (num_free_sets &&

(type == &PySet_Type || type == &PyFrozenSet_Type)) {

so = free_sets[--num_free_sets];

assert (so != NULL && PyAnySet_CheckExact(so));

so->ob_type = type;

_Py_NewReference((PyObject *)so);

EMPTY_TO_MINSIZE(so);

PyObject_GC_Track(so);

} else {

so = (PySetObject *)type->tp_alloc(type, 0);

if (so == NULL)

return NULL;

/* tp_alloc has already zeroed the structure */

assert(so->table == NULL && so->fill == 0 && so->used == 0);

INIT_NONZERO_SET_SLOTS(so);

}

so->lookup = set_lookkey_string;

so->weakreflist = NULL;

if (iterable != NULL) {

if (set_update_internal(so, iterable) == -1) {

Py_DECREF(so);

return NULL;

}

}

return (PyObject *)so;

}

/* The empty frozenset is a singleton */

static PyObject *emptyfrozenset = NULL;

static PyObject *

frozenset_new(PyTypeObject *type, PyObject *args, PyObject *kwds)

{

PyObject *iterable = NULL, *result;

if (!_PyArg_NoKeywords("frozenset()", kwds))

return NULL;

if (!PyArg_UnpackTuple(args, type->tp_name, 0, 1, &iterable))

return NULL;

if (type != &PyFrozenSet_Type)

return make_new_set(type, iterable);

if (iterable != NULL) {

/* frozenset(f) is idempotent */

if (PyFrozenSet_CheckExact(iterable)) {

Py_INCREF(iterable);

return iterable;

}

result = make_new_set(type, iterable);

if (result == NULL || PySet_GET_SIZE(result))

return result;

Py_DECREF(result);

}

/* The empty frozenset is a singleton */

if (emptyfrozenset == NULL)

emptyfrozenset = make_new_set(type, NULL);

Py_XINCREF(emptyfrozenset);

return emptyfrozenset;

}

void

PySet_Fini(void)

{

PySetObject *so;

while (num_free_sets) {

num_free_sets--;

so = free_sets[num_free_sets];

PyObject_GC_Del(so);

}

Py_CLEAR(dummy);

Py_CLEAR(emptyfrozenset);

}