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[python.git] / Objects / setobject.c

/* set object implementation 
   Written and maintained by Raymond D. Hettinger <python@rcn.com>
   Derived from Lib/sets.py and Objects/dictobject.c.

   Copyright (c) 2003-2007 Python Software Foundation.
   All rights reserved.
*/

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

/* Set a key error with the specified argument, wrapping it in a
 * tuple automatically so that tuple keys are not unpacked as the
 * exception arguments. */
static void
set_key_error(PyObject *arg)
{
        PyObject *tup;
        tup = PyTuple_Pack(1, arg);
        if (!tup)
                return; /* caller will expect error to be set anyway */
        PyErr_SetObject(PyExc_KeyError, tup);
        Py_DECREF(tup);
}

/* 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 */
#ifndef PySet_MAXFREELIST
#define PySet_MAXFREELIST 80
#endif
static PySetObject *free_list[PySet_MAXFREELIST];
static int numfree = 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;
                        Py_INCREF(startkey);
                        cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
                        Py_DECREF(startkey);
                        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;
                        Py_INCREF(startkey);
                        cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
                        Py_DECREF(startkey);
                        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;
        }
        assert(0);      /* NOT REACHED */
        return 0;
}

/*
Internal routine to insert a new key into the table.
Used 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;
}

/*
Internal routine used by set_table_resize() to insert an item which is
known to be absent from the set.  This routine also assumes that
the set contains no deleted entries.  Besides the performance benefit,
using set_insert_clean() in set_table_resize() is dangerous (SF bug #1456209).
Note that no refcounts are changed by this routine; if needed, the caller
is responsible for incref'ing `key`.
*/
static void
set_insert_clean(register PySetObject *so, PyObject *key, long hash)
{
        register size_t i;
        register size_t perturb;
        register size_t mask = (size_t)so->mask;
        setentry *table = so->table;
        register setentry *entry;

        i = hash & mask;
        entry = &table[i];
        for (perturb = hash; entry->key != NULL; perturb >>= PERTURB_SHIFT) {
                i = (i << 2) + i + perturb + 1;
                entry = &table[i & mask];
        }
        so->fill++;
        entry->key = key;
        entry->hash = hash;
        so->used++;
}

/*
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;
                        set_insert_clean(so, entry->key, entry->hash);
                }
        }

        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) {
                Py_DECREF(entry->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);
}

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 (numfree < PySet_MAXFREELIST && PyAnySet_CheckExact(so))
                free_list[numfree++] = so;
        else 
                Py_TYPE(so)->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 status = Py_ReprEnter((PyObject*)so);

        if (status != 0) {
                if (status < 0)
                        return status;
                Py_BEGIN_ALLOW_THREADS
                fprintf(fp, "%s(...)", so->ob_type->tp_name);
                Py_END_ALLOW_THREADS
                return 0;
        }        

        Py_BEGIN_ALLOW_THREADS
        fprintf(fp, "%s([", so->ob_type->tp_name);
        Py_END_ALLOW_THREADS
        while (set_next(so, &pos, &entry)) {
                Py_BEGIN_ALLOW_THREADS
                fputs(emit, fp);
                Py_END_ALLOW_THREADS
                emit = separator;
                if (PyObject_Print(entry->key, fp, 0) != 0) {
                        Py_ReprLeave((PyObject*)so);
                        return -1;
                }
        }
        Py_BEGIN_ALLOW_THREADS
        fputs("])", fp);
        Py_END_ALLOW_THREADS
        Py_ReprLeave((PyObject*)so);        
        return 0;
}

static PyObject *
set_repr(PySetObject *so)
{
        PyObject *keys, *result=NULL, *listrepr;
        int status = Py_ReprEnter((PyObject*)so);

        if (status != 0) {
                if (status < 0)
                        return NULL;
                return PyString_FromFormat("%s(...)", so->ob_type->tp_name);
        }

        keys = PySequence_List((PyObject *)so);
        if (keys == NULL)
                goto done;
        listrepr = PyObject_Repr(keys);
        Py_DECREF(keys);
        if (listrepr == NULL)
                goto done;

        result = PyString_FromFormat("%s(%s)", so->ob_type->tp_name,
                PyString_AS_STRING(listrepr));
        Py_DECREF(listrepr);
done:
        Py_ReprLeave((PyObject*)so);
        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.\n\
Raises KeyError if the set is empty.");

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_GC_Del(si);
}

static int
setiter_traverse(setiterobject *si, visitproc visit, void *arg)
{
        Py_VISIT(si->si_set);
        return 0;
}

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 = {
        PyVarObject_HEAD_INIT(&PyType_Type, 0)
        "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 | Py_TPFLAGS_HAVE_GC,/* tp_flags */
        0,                                      /* tp_doc */
        (traverseproc)setiter_traverse,         /* 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_GC_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;
        _PyObject_GC_TRACK(si);
        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_CheckExact(other)) {
                PyObject *value;
                Py_ssize_t pos = 0;
                long hash;
                Py_ssize_t dictsize = PyDict_Size(other);

                /* 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 (dictsize == -1)
                        return -1;
                if ((so->fill + dictsize)*3 >= (so->mask+1)*2) {
                        if (set_table_resize(so, (so->used + dictsize)*2) != 0)
                                return -1;
                }
                while (_PyDict_Next(other, &pos, &key, &value, &hash)) {
                        setentry an_entry;

                        an_entry.hash = hash;
                        an_entry.key = key;
                        if (set_add_entry(so, &an_entry) == -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 *args)
{
        Py_ssize_t i;

        for (i=0 ; i<PyTuple_GET_SIZE(args) ; i++) {
                PyObject *other = PyTuple_GET_ITEM(args, i);
                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 others.");

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 (numfree &&
            (type == &PySet_Type  ||  type == &PyFrozenSet_Type)) {
                so = free_list[--numfree];
                assert (so != NULL && PyAnySet_CheckExact(so));
                Py_TYPE(so) = 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 (type == &PyFrozenSet_Type && !_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 (numfree) {
                numfree--;
                so = free_list[numfree];
                PyObject_GC_Del(so);
        }
        Py_CLEAR(dummy);
        Py_CLEAR(emptyfrozenset);
}

static PyObject *
set_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
        if (type == &PySet_Type && !_PyArg_NoKeywords("set()", kwds))
                return NULL;
        
        return make_new_set(type, NULL);
}

/* set_swap_bodies() switches the contents of any two sets by moving their
   internal data pointers and, if needed, copying the internal smalltables.
   Semantically equivalent to:

     t=set(a); a.clear(); a.update(b); b.clear(); b.update(t); del t

   The function always succeeds and it leaves both objects in a stable state.
   Useful for creating temporary frozensets from sets for membership testing 
   in __contains__(), discard(), and remove().  Also useful for operations
   that update in-place (by allowing an intermediate result to be swapped 
   into one of the original inputs).
*/

static void
set_swap_bodies(PySetObject *a, PySetObject *b)
{
        Py_ssize_t t;
        setentry *u;
        setentry *(*f)(PySetObject *so, PyObject *key, long hash);
        setentry tab[PySet_MINSIZE];
        long h;

        t = a->fill;     a->fill   = b->fill;        b->fill  = t;
        t = a->used;     a->used   = b->used;        b->used  = t;
        t = a->mask;     a->mask   = b->mask;        b->mask  = t;

        u = a->table;
        if (a->table == a->smalltable)
                u = b->smalltable;
        a->table  = b->table;
        if (b->table == b->smalltable)
                a->table = a->smalltable;
        b->table = u;

        f = a->lookup;   a->lookup = b->lookup;      b->lookup = f;

        if (a->table == a->smalltable || b->table == b->smalltable) {
                memcpy(tab, a->smalltable, sizeof(tab));
                memcpy(a->smalltable, b->smalltable, sizeof(tab));
                memcpy(b->smalltable, tab, sizeof(tab));
        }

        if (PyType_IsSubtype(Py_TYPE(a), &PyFrozenSet_Type)  &&
            PyType_IsSubtype(Py_TYPE(b), &PyFrozenSet_Type)) {
                h = a->hash;     a->hash = b->hash;  b->hash = h;
        } else {
                a->hash = -1;
                b->hash = -1;
        }
}

static PyObject *
set_copy(PySetObject *so)
{
        return make_new_set(Py_TYPE(so), (PyObject *)so);
}

static PyObject *
frozenset_copy(PySetObject *so)
{
        if (PyFrozenSet_CheckExact(so)) {
                Py_INCREF(so);
                return (PyObject *)so;
        }
        return set_copy(so);
}

PyDoc_STRVAR(copy_doc, "Return a shallow copy of a set.");

static PyObject *
set_clear(PySetObject *so)
{
        set_clear_internal(so);
        Py_RETURN_NONE;
}

PyDoc_STRVAR(clear_doc, "Remove all elements from this set.");

static PyObject *
set_union(PySetObject *so, PyObject *args)
{
        PySetObject *result;
        PyObject *other;
        Py_ssize_t i;

        result = (PySetObject *)set_copy(so);
        if (result == NULL)
                return NULL;

        for (i=0 ; i<PyTuple_GET_SIZE(args) ; i++) {
                other = PyTuple_GET_ITEM(args, i);
                if ((PyObject *)so == other)
                        continue;
                if (set_update_internal(result, other) == -1) {
                        Py_DECREF(result);
                        return NULL;
                }
        }
        return (PyObject *)result;
}

PyDoc_STRVAR(union_doc,
 "Return the union of sets as a new set.\n\
\n\
(i.e. all elements that are in either set.)");

static PyObject *
set_or(PySetObject *so, PyObject *other)
{
        PySetObject *result;

        if (!PyAnySet_Check(so) || !PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }

        result = (PySetObject *)set_copy(so);
        if (result == NULL)
                return NULL;
        if ((PyObject *)so == other)
                return (PyObject *)result;
        if (set_update_internal(result, other) == -1) {
                Py_DECREF(result);
                return NULL;
        }
        return (PyObject *)result;
}

static PyObject *
set_ior(PySetObject *so, PyObject *other)
{
        if (!PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        if (set_update_internal(so, other) == -1)
                return NULL;
        Py_INCREF(so);
        return (PyObject *)so;
}

static PyObject *
set_intersection(PySetObject *so, PyObject *other)
{
        PySetObject *result;
        PyObject *key, *it, *tmp;

        if ((PyObject *)so == other)
                return set_copy(so);

        result = (PySetObject *)make_new_set(Py_TYPE(so), NULL);
        if (result == NULL)
                return NULL;

        if (PyAnySet_Check(other)) {            
                Py_ssize_t pos = 0;
                setentry *entry;

                if (PySet_GET_SIZE(other) > PySet_GET_SIZE(so)) {
                        tmp = (PyObject *)so;
                        so = (PySetObject *)other;
                        other = tmp;
                }

                while (set_next((PySetObject *)other, &pos, &entry)) {
                        int rv = set_contains_entry(so, entry);
                        if (rv == -1) {
                                Py_DECREF(result);
                                return NULL;
                        }
                        if (rv) {
                                if (set_add_entry(result, entry) == -1) {
                                        Py_DECREF(result);
                                        return NULL;
                                }
                        }
                }
                return (PyObject *)result;
        }

        it = PyObject_GetIter(other);
        if (it == NULL) {
                Py_DECREF(result);
                return NULL;
        }

        while ((key = PyIter_Next(it)) != NULL) {
                int rv;
                setentry entry;
                long hash = PyObject_Hash(key);

                if (hash == -1) {
                        Py_DECREF(it);
                        Py_DECREF(result);
                        Py_DECREF(key);
                        return NULL;
                }
                entry.hash = hash;
                entry.key = key;
                rv = set_contains_entry(so, &entry);
                if (rv == -1) {
                        Py_DECREF(it);
                        Py_DECREF(result);
                        Py_DECREF(key);
                        return NULL;
                }
                if (rv) {
                        if (set_add_entry(result, &entry) == -1) {
                                Py_DECREF(it);
                                Py_DECREF(result);
                                Py_DECREF(key);
                                return NULL;
                        }
                }
                Py_DECREF(key);
        }
        Py_DECREF(it);
        if (PyErr_Occurred()) {
                Py_DECREF(result);
                return NULL;
        }
        return (PyObject *)result;
}

static PyObject *
set_intersection_multi(PySetObject *so, PyObject *args)
{
        Py_ssize_t i;
        PyObject *result = (PyObject *)so;

        if (PyTuple_GET_SIZE(args) == 0)
                return set_copy(so);

        Py_INCREF(so);
        for (i=0 ; i<PyTuple_GET_SIZE(args) ; i++) {
                PyObject *other = PyTuple_GET_ITEM(args, i);
                PyObject *newresult = set_intersection((PySetObject *)result, other);
                if (newresult == NULL) {
                        Py_DECREF(result);
                        return NULL;
                }
                Py_DECREF(result);
                result = newresult;
        }
        return result;
}

PyDoc_STRVAR(intersection_doc,
"Return the intersection of two or more sets as a new set.\n\
\n\
(i.e. elements that are common to all of the sets.)");

static PyObject *
set_intersection_update(PySetObject *so, PyObject *other)
{
        PyObject *tmp;

        tmp = set_intersection(so, other);
        if (tmp == NULL)
                return NULL;
        set_swap_bodies(so, (PySetObject *)tmp);
        Py_DECREF(tmp);
        Py_RETURN_NONE;
}

static PyObject *
set_intersection_update_multi(PySetObject *so, PyObject *args)
{
        PyObject *tmp;

        tmp = set_intersection_multi(so, args);
        if (tmp == NULL)
                return NULL;
        set_swap_bodies(so, (PySetObject *)tmp);
        Py_DECREF(tmp);
        Py_RETURN_NONE;
}

PyDoc_STRVAR(intersection_update_doc,
"Update a set with the intersection of itself and another.");

static PyObject *
set_and(PySetObject *so, PyObject *other)
{
        if (!PyAnySet_Check(so) || !PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        return set_intersection(so, other);
}

static PyObject *
set_iand(PySetObject *so, PyObject *other)
{
        PyObject *result;

        if (!PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        result = set_intersection_update(so, other);
        if (result == NULL)
                return NULL;
        Py_DECREF(result);
        Py_INCREF(so);
        return (PyObject *)so;
}

static PyObject *
set_isdisjoint(PySetObject *so, PyObject *other)
{
        PyObject *key, *it, *tmp;

        if ((PyObject *)so == other) {
                if (PySet_GET_SIZE(so) == 0)
                        Py_RETURN_TRUE;
                else
                        Py_RETURN_FALSE;
        }

        if (PyAnySet_CheckExact(other)) {               
                Py_ssize_t pos = 0;
                setentry *entry;

                if (PySet_GET_SIZE(other) > PySet_GET_SIZE(so)) {
                        tmp = (PyObject *)so;
                        so = (PySetObject *)other;
                        other = tmp;
                }
                while (set_next((PySetObject *)other, &pos, &entry)) {
                        int rv = set_contains_entry(so, entry);
                        if (rv == -1)
                                return NULL;
                        if (rv)
                                Py_RETURN_FALSE;
                }
                Py_RETURN_TRUE;
        }

        it = PyObject_GetIter(other);
        if (it == NULL)
                return NULL;

        while ((key = PyIter_Next(it)) != NULL) {
                int rv;
                setentry entry;
                long hash = PyObject_Hash(key);

                if (hash == -1) {
                        Py_DECREF(key);
                        Py_DECREF(it);
                        return NULL;
                }
                entry.hash = hash;
                entry.key = key;
                rv = set_contains_entry(so, &entry);
                Py_DECREF(key);
                if (rv == -1) {
                        Py_DECREF(it);
                        return NULL;
                }
                if (rv) {
                        Py_DECREF(it);
                        Py_RETURN_FALSE;
                }
        }
        Py_DECREF(it);
        if (PyErr_Occurred())
                return NULL;
        Py_RETURN_TRUE;
}

PyDoc_STRVAR(isdisjoint_doc,
"Return True if two sets have a null intersection.");

static int
set_difference_update_internal(PySetObject *so, PyObject *other)
{
        if ((PyObject *)so == other)
                return set_clear_internal(so);
        
        if (PyAnySet_Check(other)) {
                setentry *entry;
                Py_ssize_t pos = 0;

                while (set_next((PySetObject *)other, &pos, &entry))
                        if (set_discard_entry(so, entry) == -1)
                                return -1;
        } else {
                PyObject *key, *it;
                it = PyObject_GetIter(other);
                if (it == NULL)
                        return -1;

                while ((key = PyIter_Next(it)) != NULL) {
                        if (set_discard_key(so, key) == -1) {
                                Py_DECREF(it);
                                Py_DECREF(key);
                                return -1;
                        }
                        Py_DECREF(key);
                }
                Py_DECREF(it);
                if (PyErr_Occurred())
                        return -1;
        }
        /* If more than 1/5 are dummies, then resize them away. */
        if ((so->fill - so->used) * 5 < so->mask)
                return 0;
        return set_table_resize(so, so->used>50000 ? so->used*2 : so->used*4);
}

static PyObject *
set_difference_update(PySetObject *so, PyObject *args)
{
        Py_ssize_t i;

        for (i=0 ; i<PyTuple_GET_SIZE(args) ; i++) {
                PyObject *other = PyTuple_GET_ITEM(args, i);
                if (set_difference_update_internal(so, other) == -1)
                        return NULL;
        }
        Py_RETURN_NONE;
}

PyDoc_STRVAR(difference_update_doc,
"Remove all elements of another set from this set.");

static PyObject *
set_difference(PySetObject *so, PyObject *other)
{
        PyObject *result;
        setentry *entry;
        Py_ssize_t pos = 0;

        if (!PyAnySet_Check(other)  && !PyDict_CheckExact(other)) {
                result = set_copy(so);
                if (result == NULL)
                        return NULL;
                if (set_difference_update_internal((PySetObject *)result, other) != -1)
                        return result;
                Py_DECREF(result);
                return NULL;
        }
        
        result = make_new_set(Py_TYPE(so), NULL);
        if (result == NULL)
                return NULL;

        if (PyDict_CheckExact(other)) {
                while (set_next(so, &pos, &entry)) {
                        setentry entrycopy;
                        entrycopy.hash = entry->hash;
                        entrycopy.key = entry->key;
                        if (!_PyDict_Contains(other, entry->key, entry->hash)) {
                                if (set_add_entry((PySetObject *)result, &entrycopy) == -1) {
                                        Py_DECREF(result);
                                        return NULL;
                                }
                        }
                }
                return result;
        }

        while (set_next(so, &pos, &entry)) {
                int rv = set_contains_entry((PySetObject *)other, entry);
                if (rv == -1) {
                        Py_DECREF(result);
                        return NULL;
                }
                if (!rv) {
                        if (set_add_entry((PySetObject *)result, entry) == -1) {
                                Py_DECREF(result);
                                return NULL;
                        }
                }
        }
        return result;
}

static PyObject *
set_difference_multi(PySetObject *so, PyObject *args)
{
        Py_ssize_t i;
        PyObject *result, *other;

        if (PyTuple_GET_SIZE(args) == 0)
                return set_copy(so);

        other = PyTuple_GET_ITEM(args, 0);
        result = set_difference(so, other);
        if (result == NULL)
                return NULL;

        for (i=1 ; i<PyTuple_GET_SIZE(args) ; i++) {
                other = PyTuple_GET_ITEM(args, i);
                if (set_difference_update_internal((PySetObject *)result, other) == -1) {
                        Py_DECREF(result);
                        return NULL;
                }
        }
        return result;
}

PyDoc_STRVAR(difference_doc,
"Return the difference of two or more sets as a new set.\n\
\n\
(i.e. all elements that are in this set but not the others.)");
static PyObject *
set_sub(PySetObject *so, PyObject *other)
{
        if (!PyAnySet_Check(so) || !PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        return set_difference(so, other);
}

static PyObject *
set_isub(PySetObject *so, PyObject *other)
{
        if (!PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        if (set_difference_update_internal(so, other) == -1)
                return NULL;
        Py_INCREF(so);
        return (PyObject *)so;
}

static PyObject *
set_symmetric_difference_update(PySetObject *so, PyObject *other)
{
        PySetObject *otherset;
        PyObject *key;
        Py_ssize_t pos = 0;
        setentry *entry;

        if ((PyObject *)so == other)
                return set_clear(so);

        if (PyDict_CheckExact(other)) {
                PyObject *value;
                int rv;
                long hash;
                while (_PyDict_Next(other, &pos, &key, &value, &hash)) {
                        setentry an_entry;

                        an_entry.hash = hash;
                        an_entry.key = key;
                        rv = set_discard_entry(so, &an_entry);
                        if (rv == -1)
                                return NULL;
                        if (rv == DISCARD_NOTFOUND) {
                                if (set_add_entry(so, &an_entry) == -1)
                                        return NULL;
                        }
                }
                Py_RETURN_NONE;
        }

        if (PyAnySet_Check(other)) {
                Py_INCREF(other);
                otherset = (PySetObject *)other;
        } else {
                otherset = (PySetObject *)make_new_set(Py_TYPE(so), other);
                if (otherset == NULL)
                        return NULL;
        }

        while (set_next(otherset, &pos, &entry)) {
                int rv = set_discard_entry(so, entry);
                if (rv == -1) {
                        Py_DECREF(otherset);
                        return NULL;
                }
                if (rv == DISCARD_NOTFOUND) {
                        if (set_add_entry(so, entry) == -1) {
                                Py_DECREF(otherset);
                                return NULL;
                        }
                }
        }
        Py_DECREF(otherset);
        Py_RETURN_NONE;
}

PyDoc_STRVAR(symmetric_difference_update_doc,
"Update a set with the symmetric difference of itself and another.");

static PyObject *
set_symmetric_difference(PySetObject *so, PyObject *other)
{
        PyObject *rv;
        PySetObject *otherset;

        otherset = (PySetObject *)make_new_set(Py_TYPE(so), other);
        if (otherset == NULL)
                return NULL;
        rv = set_symmetric_difference_update(otherset, (PyObject *)so);
        if (rv == NULL)
                return NULL;
        Py_DECREF(rv);
        return (PyObject *)otherset;
}

PyDoc_STRVAR(symmetric_difference_doc,
"Return the symmetric difference of two sets as a new set.\n\
\n\
(i.e. all elements that are in exactly one of the sets.)");

static PyObject *
set_xor(PySetObject *so, PyObject *other)
{
        if (!PyAnySet_Check(so) || !PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        return set_symmetric_difference(so, other);
}

static PyObject *
set_ixor(PySetObject *so, PyObject *other)
{
        PyObject *result;

        if (!PyAnySet_Check(other)) {
                Py_INCREF(Py_NotImplemented);
                return Py_NotImplemented;
        }
        result = set_symmetric_difference_update(so, other);
        if (result == NULL)
                return NULL;
        Py_DECREF(result);
        Py_INCREF(so);
        return (PyObject *)so;
}

static PyObject *
set_issubset(PySetObject *so, PyObject *other)
{
        setentry *entry;
        Py_ssize_t pos = 0;

        if (!PyAnySet_Check(other)) {
                PyObject *tmp, *result;
                tmp = make_new_set(&PySet_Type, other);
                if (tmp == NULL)
                        return NULL;
                result = set_issubset(so, tmp);
                Py_DECREF(tmp);
                return result;
        }
        if (PySet_GET_SIZE(so) > PySet_GET_SIZE(other)) 
                Py_RETURN_FALSE;

        while (set_next(so, &pos, &entry)) {
                int rv = set_contains_entry((PySetObject *)other, entry);
                if (rv == -1)
                        return NULL;
                if (!rv)
                        Py_RETURN_FALSE;
        }
        Py_RETURN_TRUE;
}

PyDoc_STRVAR(issubset_doc, "Report whether another set contains this set.");

static PyObject *
set_issuperset(PySetObject *so, PyObject *other)
{
        PyObject *tmp, *result;

        if (!PyAnySet_Check(other)) {
                tmp = make_new_set(&PySet_Type, other);
                if (tmp == NULL)
                        return NULL;
                result = set_issuperset(so, tmp);
                Py_DECREF(tmp);
                return result;
        }
        return set_issubset((PySetObject *)other, (PyObject *)so);
}

PyDoc_STRVAR(issuperset_doc, "Report whether this set contains another set.");

static PyObject *
set_richcompare(PySetObject *v, PyObject *w, int op)
{
        PyObject *r1, *r2;

        if(!PyAnySet_Check(w)) {
                if (op == Py_EQ)
                        Py_RETURN_FALSE;
                if (op == Py_NE)
                        Py_RETURN_TRUE;
                PyErr_SetString(PyExc_TypeError, "can only compare to a set");
                return NULL;
        }
        switch (op) {
        case Py_EQ:
                if (PySet_GET_SIZE(v) != PySet_GET_SIZE(w))
                        Py_RETURN_FALSE;
                if (v->hash != -1  &&
                    ((PySetObject *)w)->hash != -1 &&
                    v->hash != ((PySetObject *)w)->hash)
                        Py_RETURN_FALSE;
                return set_issubset(v, w);
        case Py_NE:
                r1 = set_richcompare(v, w, Py_EQ);
                if (r1 == NULL)
                        return NULL;
                r2 = PyBool_FromLong(PyObject_Not(r1));
                Py_DECREF(r1);
                return r2;
        case Py_LE:
                return set_issubset(v, w);
        case Py_GE:
                return set_issuperset(v, w);
        case Py_LT:
                if (PySet_GET_SIZE(v) >= PySet_GET_SIZE(w))
                        Py_RETURN_FALSE;                
                return set_issubset(v, w);
        case Py_GT:
                if (PySet_GET_SIZE(v) <= PySet_GET_SIZE(w))
                        Py_RETURN_FALSE;
                return set_issuperset(v, w);
        }
        Py_INCREF(Py_NotImplemented);
        return Py_NotImplemented;
}

static int
set_nocmp(PyObject *self, PyObject *other)
{
        PyErr_SetString(PyExc_TypeError, "cannot compare sets using cmp()");
        return -1;
}

static PyObject *
set_add(PySetObject *so, PyObject *key)
{
        if (set_add_key(so, key) == -1)
                return NULL;
        Py_RETURN_NONE;
}

PyDoc_STRVAR(add_doc, 
"Add an element to a set.\n\
\n\
This has no effect if the element is already present.");

static int
set_contains(PySetObject *so, PyObject *key)
{
        PyObject *tmpkey;
        int rv;

        rv = set_contains_key(so, key);
        if (rv == -1) {
                if (!PySet_Check(key) || !PyErr_ExceptionMatches(PyExc_TypeError))
                        return -1;
                PyErr_Clear();
                tmpkey = make_new_set(&PyFrozenSet_Type, NULL);
                if (tmpkey == NULL)
                        return -1;
                set_swap_bodies((PySetObject *)tmpkey, (PySetObject *)key);
                rv = set_contains(so, tmpkey);
                set_swap_bodies((PySetObject *)tmpkey, (PySetObject *)key);
                Py_DECREF(tmpkey);
        }
        return rv;
}

static PyObject *
set_direct_contains(PySetObject *so, PyObject *key)
{
        long result;

        result = set_contains(so, key);
        if (result == -1)
                return NULL;
        return PyBool_FromLong(result);
}

PyDoc_STRVAR(contains_doc, "x.__contains__(y) <==> y in x.");

static PyObject *
set_remove(PySetObject *so, PyObject *key)
{
        PyObject *tmpkey;
        int rv;

        rv = set_discard_key(so, key);
        if (rv == -1) {
                if (!PySet_Check(key) || !PyErr_ExceptionMatches(PyExc_TypeError))
                        return NULL;
                PyErr_Clear();
                tmpkey = make_new_set(&PyFrozenSet_Type, NULL);
                if (tmpkey == NULL)
                        return NULL;
                set_swap_bodies((PySetObject *)tmpkey, (PySetObject *)key);
                rv = set_discard_key(so, tmpkey);
                set_swap_bodies((PySetObject *)tmpkey, (PySetObject *)key);
                Py_DECREF(tmpkey);
                if (rv == -1)
                        return NULL;
        } 

        if (rv == DISCARD_NOTFOUND) {
                set_key_error(key);
                return NULL;
        }
        Py_RETURN_NONE;
}

PyDoc_STRVAR(remove_doc,
"Remove an element from a set; it must be a member.\n\
\n\
If the element is not a member, raise a KeyError.");

static PyObject *
set_discard(PySetObject *so, PyObject *key)
{
        PyObject *tmpkey, *result;
        int rv;

        rv = set_discard_key(so, key);
        if (rv == -1) {
                if (!PySet_Check(key) || !PyErr_ExceptionMatches(PyExc_TypeError))
                        return NULL;
                PyErr_Clear();
                tmpkey = make_new_set(&PyFrozenSet_Type, NULL);
                if (tmpkey == NULL)
                        return NULL;
                set_swap_bodies((PySetObject *)tmpkey, (PySetObject *)key);
                result = set_discard(so, tmpkey);
                set_swap_bodies((PySetObject *)tmpkey, (PySetObject *)key);
                Py_DECREF(tmpkey);
                return result;
        }
        Py_RETURN_NONE;
}

PyDoc_STRVAR(discard_doc,
"Remove an element from a set if it is a member.\n\
\n\
If the element is not a member, do nothing."); 

static PyObject *
set_reduce(PySetObject *so)
{
        PyObject *keys=NULL, *args=NULL, *result=NULL, *dict=NULL;

        keys = PySequence_List((PyObject *)so);
        if (keys == NULL)
                goto done;
        args = PyTuple_Pack(1, keys);
        if (args == NULL)
                goto done;
        dict = PyObject_GetAttrString((PyObject *)so, "__dict__");
        if (dict == NULL) {
                PyErr_Clear();
                dict = Py_None;
                Py_INCREF(dict);
        }
        result = PyTuple_Pack(3, Py_TYPE(so), args, dict);
done:
        Py_XDECREF(args);
        Py_XDECREF(keys);
        Py_XDECREF(dict);
        return result;
}

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

static PyObject *
set_sizeof(PySetObject *so)
{
        Py_ssize_t res;

        res = sizeof(PySetObject);
        if (so->table != so->smalltable)
                res = res + (so->mask + 1) * sizeof(setentry);
        return PyInt_FromSsize_t(res);
}

PyDoc_STRVAR(sizeof_doc, "S.__sizeof__() -> size of S in memory, in bytes");
static int
set_init(PySetObject *self, PyObject *args, PyObject *kwds)
{
        PyObject *iterable = NULL;

        if (!PyAnySet_Check(self))
                return -1;
        if (!PyArg_UnpackTuple(args, Py_TYPE(self)->tp_name, 0, 1, &iterable))
                return -1;
        set_clear_internal(self);
        self->hash = -1;
        if (iterable == NULL)
                return 0;
        return set_update_internal(self, iterable);
}

static PySequenceMethods set_as_sequence = {
        set_len,                        /* sq_length */
        0,                              /* sq_concat */
        0,                              /* sq_repeat */
        0,                              /* sq_item */
        0,                              /* sq_slice */
        0,                              /* sq_ass_item */
        0,                              /* sq_ass_slice */
        (objobjproc)set_contains,       /* sq_contains */
};

/* set object ********************************************************/

#ifdef Py_DEBUG
static PyObject *test_c_api(PySetObject *so);

PyDoc_STRVAR(test_c_api_doc, "Exercises C API.  Returns True.\n\
All is well if assertions don't fail.");
#endif

static PyMethodDef set_methods[] = {
        {"add",         (PyCFunction)set_add,           METH_O,
         add_doc},
        {"clear",       (PyCFunction)set_clear,         METH_NOARGS,
         clear_doc},
        {"__contains__",(PyCFunction)set_direct_contains,       METH_O | METH_COEXIST,
         contains_doc},
        {"copy",        (PyCFunction)set_copy,          METH_NOARGS,
         copy_doc},
        {"discard",     (PyCFunction)set_discard,       METH_O,
         discard_doc},
        {"difference",  (PyCFunction)set_difference_multi,      METH_VARARGS,
         difference_doc},
        {"difference_update",   (PyCFunction)set_difference_update,     METH_VARARGS,
         difference_update_doc},
        {"intersection",(PyCFunction)set_intersection_multi,    METH_VARARGS,
         intersection_doc},
        {"intersection_update",(PyCFunction)set_intersection_update_multi,      METH_VARARGS,
         intersection_update_doc},
        {"isdisjoint",  (PyCFunction)set_isdisjoint,    METH_O,
         isdisjoint_doc},
        {"issubset",    (PyCFunction)set_issubset,      METH_O,
         issubset_doc},
        {"issuperset",  (PyCFunction)set_issuperset,    METH_O,
         issuperset_doc},
        {"pop",         (PyCFunction)set_pop,           METH_NOARGS,
         pop_doc},
        {"__reduce__",  (PyCFunction)set_reduce,        METH_NOARGS,
         reduce_doc},
        {"remove",      (PyCFunction)set_remove,        METH_O,
         remove_doc},
        {"__sizeof__",  (PyCFunction)set_sizeof,        METH_NOARGS,
         sizeof_doc},
        {"symmetric_difference",(PyCFunction)set_symmetric_difference,  METH_O,
         symmetric_difference_doc},
        {"symmetric_difference_update",(PyCFunction)set_symmetric_difference_update,    METH_O,
         symmetric_difference_update_doc},
#ifdef Py_DEBUG
        {"test_c_api",  (PyCFunction)test_c_api,        METH_NOARGS,
         test_c_api_doc},
#endif
        {"union",       (PyCFunction)set_union,         METH_VARARGS,
         union_doc},
        {"update",      (PyCFunction)set_update,        METH_VARARGS,
         update_doc},
        {NULL,          NULL}   /* sentinel */
};

static PyNumberMethods set_as_number = {
        0,                              /*nb_add*/
        (binaryfunc)set_sub,            /*nb_subtract*/
        0,                              /*nb_multiply*/
        0,                              /*nb_divide*/
        0,                              /*nb_remainder*/
        0,                              /*nb_divmod*/
        0,                              /*nb_power*/
        0,                              /*nb_negative*/
        0,                              /*nb_positive*/
        0,                              /*nb_absolute*/
        0,                              /*nb_nonzero*/
        0,                              /*nb_invert*/
        0,                              /*nb_lshift*/
        0,                              /*nb_rshift*/
        (binaryfunc)set_and,            /*nb_and*/
        (binaryfunc)set_xor,            /*nb_xor*/
        (binaryfunc)set_or,             /*nb_or*/
        0,                              /*nb_coerce*/
        0,                              /*nb_int*/
        0,                              /*nb_long*/
        0,                              /*nb_float*/
        0,                              /*nb_oct*/
        0,                              /*nb_hex*/
        0,                              /*nb_inplace_add*/
        (binaryfunc)set_isub,           /*nb_inplace_subtract*/
        0,                              /*nb_inplace_multiply*/
        0,                              /*nb_inplace_divide*/
        0,                              /*nb_inplace_remainder*/
        0,                              /*nb_inplace_power*/
        0,                              /*nb_inplace_lshift*/
        0,                              /*nb_inplace_rshift*/
        (binaryfunc)set_iand,           /*nb_inplace_and*/
        (binaryfunc)set_ixor,           /*nb_inplace_xor*/
        (binaryfunc)set_ior,            /*nb_inplace_or*/
};

PyDoc_STRVAR(set_doc,
"set(iterable) --> set object\n\
\n\
Build an unordered collection of unique elements.");

PyTypeObject PySet_Type = {
        PyVarObject_HEAD_INIT(&PyType_Type, 0)
        "set",                          /* tp_name */
        sizeof(PySetObject),            /* tp_basicsize */
        0,                              /* tp_itemsize */
        /* methods */
        (destructor)set_dealloc,        /* tp_dealloc */
        (printfunc)set_tp_print,        /* tp_print */
        0,                              /* tp_getattr */
        0,                              /* tp_setattr */
        set_nocmp,                      /* tp_compare */
        (reprfunc)set_repr,             /* tp_repr */
        &set_as_number,                 /* tp_as_number */
        &set_as_sequence,               /* tp_as_sequence */
        0,                              /* tp_as_mapping */
        (hashfunc)PyObject_HashNotImplemented,  /* 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_CHECKTYPES |
                Py_TPFLAGS_BASETYPE,    /* tp_flags */
        set_doc,                        /* tp_doc */
        (traverseproc)set_traverse,     /* tp_traverse */
        (inquiry)set_clear_internal,    /* tp_clear */
        (richcmpfunc)set_richcompare,   /* tp_richcompare */
        offsetof(PySetObject, weakreflist),     /* tp_weaklistoffset */
        (getiterfunc)set_iter,  /* tp_iter */
        0,                              /* tp_iternext */
        set_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 */
        (initproc)set_init,             /* tp_init */
        PyType_GenericAlloc,            /* tp_alloc */
        set_new,                        /* tp_new */
        PyObject_GC_Del,                /* tp_free */
};

/* frozenset object ********************************************************/


static PyMethodDef frozenset_methods[] = {
        {"__contains__",(PyCFunction)set_direct_contains,       METH_O | METH_COEXIST,
         contains_doc},
        {"copy",        (PyCFunction)frozenset_copy,    METH_NOARGS,
         copy_doc},
        {"difference",  (PyCFunction)set_difference_multi,      METH_VARARGS,
         difference_doc},
        {"intersection",(PyCFunction)set_intersection_multi,    METH_VARARGS,
         intersection_doc},
        {"isdisjoint",  (PyCFunction)set_isdisjoint,    METH_O,
         isdisjoint_doc},
        {"issubset",    (PyCFunction)set_issubset,      METH_O,
         issubset_doc},
        {"issuperset",  (PyCFunction)set_issuperset,    METH_O,
         issuperset_doc},
        {"__reduce__",  (PyCFunction)set_reduce,        METH_NOARGS,
         reduce_doc},
        {"__sizeof__",  (PyCFunction)set_sizeof,        METH_NOARGS,
         sizeof_doc},
        {"symmetric_difference",(PyCFunction)set_symmetric_difference,  METH_O,
         symmetric_difference_doc},
        {"union",       (PyCFunction)set_union,         METH_VARARGS,
         union_doc},
        {NULL,          NULL}   /* sentinel */
};

static PyNumberMethods frozenset_as_number = {
        0,                              /*nb_add*/
        (binaryfunc)set_sub,            /*nb_subtract*/
        0,                              /*nb_multiply*/
        0,                              /*nb_divide*/
        0,                              /*nb_remainder*/
        0,                              /*nb_divmod*/
        0,                              /*nb_power*/
        0,                              /*nb_negative*/
        0,                              /*nb_positive*/
        0,                              /*nb_absolute*/
        0,                              /*nb_nonzero*/
        0,                              /*nb_invert*/
        0,                              /*nb_lshift*/
        0,                              /*nb_rshift*/
        (binaryfunc)set_and,            /*nb_and*/
        (binaryfunc)set_xor,            /*nb_xor*/
        (binaryfunc)set_or,             /*nb_or*/
};

PyDoc_STRVAR(frozenset_doc,
"frozenset(iterable) --> frozenset object\n\
\n\
Build an immutable unordered collection of unique elements.");

PyTypeObject PyFrozenSet_Type = {
        PyVarObject_HEAD_INIT(&PyType_Type, 0)
        "frozenset",                    /* tp_name */
        sizeof(PySetObject),            /* tp_basicsize */
        0,                              /* tp_itemsize */
        /* methods */
        (destructor)set_dealloc,        /* tp_dealloc */
        (printfunc)set_tp_print,        /* tp_print */
        0,                              /* tp_getattr */
        0,                              /* tp_setattr */
        set_nocmp,                      /* tp_compare */
        (reprfunc)set_repr,             /* tp_repr */
        &frozenset_as_number,           /* tp_as_number */
        &set_as_sequence,               /* tp_as_sequence */
        0,                              /* tp_as_mapping */
        frozenset_hash,                 /* 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_CHECKTYPES |
                Py_TPFLAGS_BASETYPE,    /* tp_flags */
        frozenset_doc,                  /* tp_doc */
        (traverseproc)set_traverse,     /* tp_traverse */
        (inquiry)set_clear_internal,    /* tp_clear */
        (richcmpfunc)set_richcompare,   /* tp_richcompare */
        offsetof(PySetObject, weakreflist),     /* tp_weaklistoffset */
        (getiterfunc)set_iter,          /* tp_iter */
        0,                              /* tp_iternext */
        frozenset_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 */
        PyType_GenericAlloc,            /* tp_alloc */
        frozenset_new,                  /* tp_new */
        PyObject_GC_Del,                /* tp_free */
};


/***** C API functions *************************************************/

PyObject *
PySet_New(PyObject *iterable)
{
        return make_new_set(&PySet_Type, iterable);
}

PyObject *
PyFrozenSet_New(PyObject *iterable)
{
        return make_new_set(&PyFrozenSet_Type, iterable);
}

Py_ssize_t
PySet_Size(PyObject *anyset)
{
        if (!PyAnySet_Check(anyset)) {
                PyErr_BadInternalCall();
                return -1;
        }
        return PySet_GET_SIZE(anyset);
}

int
PySet_Clear(PyObject *set)
{
        if (!PySet_Check(set)) {
                PyErr_BadInternalCall();
                return -1;
        }
        return set_clear_internal((PySetObject *)set);
}

int
PySet_Contains(PyObject *anyset, PyObject *key)
{
        if (!PyAnySet_Check(anyset)) {
                PyErr_BadInternalCall();
                return -1;
        }
        return set_contains_key((PySetObject *)anyset, key);
}

int
PySet_Discard(PyObject *set, PyObject *key)
{
        if (!PySet_Check(set)) {
                PyErr_BadInternalCall();
                return -1;
        }
        return set_discard_key((PySetObject *)set, key);
}

int
PySet_Add(PyObject *anyset, PyObject *key)
{
        if (!PySet_Check(anyset) && 
            (!PyFrozenSet_Check(anyset) || Py_REFCNT(anyset) != 1)) {
                PyErr_BadInternalCall();
                return -1;
        }
        return set_add_key((PySetObject *)anyset, key);
}

int
_PySet_Next(PyObject *set, Py_ssize_t *pos, PyObject **key)
{
        setentry *entry_ptr;

        if (!PyAnySet_Check(set)) {
                PyErr_BadInternalCall();
                return -1;
        }
        if (set_next((PySetObject *)set, pos, &entry_ptr) == 0)
                return 0;
        *key = entry_ptr->key;
        return 1;
}

int
_PySet_NextEntry(PyObject *set, Py_ssize_t *pos, PyObject **key, long *hash)
{
        setentry *entry;

        if (!PyAnySet_Check(set)) {
                PyErr_BadInternalCall();
                return -1;
        }
        if (set_next((PySetObject *)set, pos, &entry) == 0)
                return 0;
        *key = entry->key;
        *hash = entry->hash;
        return 1;
}

PyObject *
PySet_Pop(PyObject *set)
{
        if (!PySet_Check(set)) {
                PyErr_BadInternalCall();
                return NULL;
        }
        return set_pop((PySetObject *)set);
}

int
_PySet_Update(PyObject *set, PyObject *iterable)
{
        if (!PySet_Check(set)) {
                PyErr_BadInternalCall();
                return -1;
        }
        return set_update_internal((PySetObject *)set, iterable);
}

#ifdef Py_DEBUG

/* Test code to be called with any three element set. 
   Returns True and original set is restored. */

#define assertRaises(call_return_value, exception)              \
        do {                                                    \
                assert(call_return_value);                      \
                assert(PyErr_ExceptionMatches(exception));      \
                PyErr_Clear();                                  \
        } while(0)

static PyObject *
test_c_api(PySetObject *so)
{
        Py_ssize_t count;
        char *s;
        Py_ssize_t i;
        PyObject *elem=NULL, *dup=NULL, *t, *f, *dup2, *x;
        PyObject *ob = (PyObject *)so;

        /* Verify preconditions and exercise type/size checks */
        assert(PyAnySet_Check(ob));
        assert(PyAnySet_CheckExact(ob));
        assert(!PyFrozenSet_CheckExact(ob));
        assert(PySet_Size(ob) == 3);
        assert(PySet_GET_SIZE(ob) == 3);

        /* Raise TypeError for non-iterable constructor arguments */
        assertRaises(PySet_New(Py_None) == NULL, PyExc_TypeError);
        assertRaises(PyFrozenSet_New(Py_None) == NULL, PyExc_TypeError);

        /* Raise TypeError for unhashable key */
        dup = PySet_New(ob);
        assertRaises(PySet_Discard(ob, dup) == -1, PyExc_TypeError);
        assertRaises(PySet_Contains(ob, dup) == -1, PyExc_TypeError);
        assertRaises(PySet_Add(ob, dup) == -1, PyExc_TypeError);

        /* Exercise successful pop, contains, add, and discard */
        elem = PySet_Pop(ob);
        assert(PySet_Contains(ob, elem) == 0);
        assert(PySet_GET_SIZE(ob) == 2);
        assert(PySet_Add(ob, elem) == 0);
        assert(PySet_Contains(ob, elem) == 1);
        assert(PySet_GET_SIZE(ob) == 3);
        assert(PySet_Discard(ob, elem) == 1);
        assert(PySet_GET_SIZE(ob) == 2);
        assert(PySet_Discard(ob, elem) == 0);
        assert(PySet_GET_SIZE(ob) == 2);

        /* Exercise clear */
        dup2 = PySet_New(dup);
        assert(PySet_Clear(dup2) == 0);
        assert(PySet_Size(dup2) == 0);
        Py_DECREF(dup2);

        /* Raise SystemError on clear or update of frozen set */
        f = PyFrozenSet_New(dup);
        assertRaises(PySet_Clear(f) == -1, PyExc_SystemError);
        assertRaises(_PySet_Update(f, dup) == -1, PyExc_SystemError);
        assert(PySet_Add(f, elem) == 0);
        Py_INCREF(f);
        assertRaises(PySet_Add(f, elem) == -1, PyExc_SystemError);
        Py_DECREF(f);
        Py_DECREF(f);

        /* Exercise direct iteration */
        i = 0, count = 0;
        while (_PySet_Next((PyObject *)dup, &i, &x)) {
                s = PyString_AsString(x);
                assert(s && (s[0] == 'a' || s[0] == 'b' || s[0] == 'c'));
                count++;
        }
        assert(count == 3);

        /* Exercise updates */
        dup2 = PySet_New(NULL);
        assert(_PySet_Update(dup2, dup) == 0);
        assert(PySet_Size(dup2) == 3);
        assert(_PySet_Update(dup2, dup) == 0);
        assert(PySet_Size(dup2) == 3);
        Py_DECREF(dup2);

        /* Raise SystemError when self argument is not a set or frozenset. */
        t = PyTuple_New(0);
        assertRaises(PySet_Size(t) == -1, PyExc_SystemError);
        assertRaises(PySet_Contains(t, elem) == -1, PyExc_SystemError);
        Py_DECREF(t);

        /* Raise SystemError when self argument is not a set. */
        f = PyFrozenSet_New(dup);
        assert(PySet_Size(f) == 3);
        assert(PyFrozenSet_CheckExact(f));
        assertRaises(PySet_Discard(f, elem) == -1, PyExc_SystemError);
        assertRaises(PySet_Pop(f) == NULL, PyExc_SystemError);
        Py_DECREF(f);

        /* Raise KeyError when popping from an empty set */
        assert(PyNumber_InPlaceSubtract(ob, ob) == ob);
        Py_DECREF(ob);
        assert(PySet_GET_SIZE(ob) == 0);
        assertRaises(PySet_Pop(ob) == NULL, PyExc_KeyError);

        /* Restore the set from the copy using the PyNumber API */
        assert(PyNumber_InPlaceOr(ob, dup) == ob);
        Py_DECREF(ob);

        /* Verify constructors accept NULL arguments */
        f = PySet_New(NULL);
        assert(f != NULL);
        assert(PySet_GET_SIZE(f) == 0);
        Py_DECREF(f);
        f = PyFrozenSet_New(NULL);
        assert(f != NULL);
        assert(PyFrozenSet_CheckExact(f));
        assert(PySet_GET_SIZE(f) == 0);
        Py_DECREF(f);

        Py_DECREF(elem);
        Py_DECREF(dup);
        Py_RETURN_TRUE;
}

#undef assertRaises

#endif