cpython/Objects/object.c

/***********************************************************
Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam,
The Netherlands.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation, and that the names of Stichting Mathematisch
Centrum or CWI or Corporation for National Research Initiatives or
CNRI not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior
permission.

While CWI is the initial source for this software, a modified version
is made available by the Corporation for National Research Initiatives
(CNRI) at the Internet address ftp://ftp.python.org.

STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH
CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.

******************************************************************/

/* Generic object operations; and implementation of None (NoObject) */

#include "Python.h"

/* just for trashcan: */
#include "compile.h"
#include "frameobject.h"
#include "traceback.h"

#if defined( Py_TRACE_REFS ) || defined( Py_REF_DEBUG )
DL_IMPORT(long) _Py_RefTotal;
#endif

/* Object allocation routines used by NEWOBJ and NEWVAROBJ macros.
   These are used by the individual routines for object creation.
   Do not call them otherwise, they do not initialize the object! */

#ifdef COUNT_ALLOCS
static PyTypeObject *type_list;
extern int tuple_zero_allocs, fast_tuple_allocs;
extern int quick_int_allocs, quick_neg_int_allocs;
extern int null_strings, one_strings;
void
dump_counts()
{
	PyTypeObject *tp;

	for (tp = type_list; tp; tp = tp->tp_next)
		fprintf(stderr, "%s alloc'd: %d, freed: %d, max in use: %d\n",
			tp->tp_name, tp->tp_alloc, tp->tp_free,
			tp->tp_maxalloc);
	fprintf(stderr, "fast tuple allocs: %d, empty: %d\n",
		fast_tuple_allocs, tuple_zero_allocs);
	fprintf(stderr, "fast int allocs: pos: %d, neg: %d\n",
		quick_int_allocs, quick_neg_int_allocs);
	fprintf(stderr, "null strings: %d, 1-strings: %d\n",
		null_strings, one_strings);
}

PyObject *
get_counts()
{
	PyTypeObject *tp;
	PyObject *result;
	PyObject *v;

	result = PyList_New(0);
	if (result == NULL)
		return NULL;
	for (tp = type_list; tp; tp = tp->tp_next) {
		v = Py_BuildValue("(siii)", tp->tp_name, tp->tp_alloc,
				  tp->tp_free, tp->tp_maxalloc);
		if (v == NULL) {
			Py_DECREF(result);
			return NULL;
		}
		if (PyList_Append(result, v) < 0) {
			Py_DECREF(v);
			Py_DECREF(result);
			return NULL;
		}
		Py_DECREF(v);
	}
	return result;
}

void
inc_count(tp)
	PyTypeObject *tp;
{
	if (tp->tp_alloc == 0) {
		/* first time; insert in linked list */
		if (tp->tp_next != NULL) /* sanity check */
			Py_FatalError("XXX inc_count sanity check");
		tp->tp_next = type_list;
		type_list = tp;
	}
	tp->tp_alloc++;
	if (tp->tp_alloc - tp->tp_free > tp->tp_maxalloc)
		tp->tp_maxalloc = tp->tp_alloc - tp->tp_free;
}
#endif

#ifndef MS_COREDLL
PyObject *
_PyObject_New(tp)
	PyTypeObject *tp;
#else
PyObject *
_PyObject_New(tp,op)
	PyTypeObject *tp;
	PyObject *op;
#endif
{
#ifndef MS_COREDLL
	PyObject *op = (PyObject *) malloc(tp->tp_basicsize);
#endif
	if (op == NULL)
		return PyErr_NoMemory();
	op->ob_type = tp;
	_Py_NewReference(op);
	return op;
}

#ifndef MS_COREDLL
PyVarObject *
_PyObject_NewVar(tp, size)
	PyTypeObject *tp;
	int size;
#else
PyVarObject *
_PyObject_NewVar(tp, size, op)
	PyTypeObject *tp;
	int size;
	PyVarObject *op;
#endif
{
#ifndef MS_COREDLL
	PyVarObject *op = (PyVarObject *)
		malloc(tp->tp_basicsize + size * tp->tp_itemsize);
#endif
	if (op == NULL)
		return (PyVarObject *)PyErr_NoMemory();
	op->ob_type = tp;
	op->ob_size = size;
	_Py_NewReference((PyObject *)op);
	return op;
}

int
PyObject_Print(op, fp, flags)
	PyObject *op;
	FILE *fp;
	int flags;
{
	int ret = 0;
	if (PyErr_CheckSignals())
		return -1;
#ifdef USE_STACKCHECK
	if (PyOS_CheckStack()) {
		PyErr_SetString(PyExc_MemoryError, "Stack overflow");
		return -1;
	}
#endif
	clearerr(fp); /* Clear any previous error condition */
	if (op == NULL) {
		fprintf(fp, "<nil>");
	}
	else {
		if (op->ob_refcnt <= 0)
			fprintf(fp, "<refcnt %u at %lx>",
				op->ob_refcnt, (long)op);
		else if (op->ob_type->tp_print == NULL) {
			if (op->ob_type->tp_repr == NULL) {
				fprintf(fp, "<%s object at %lx>",
					op->ob_type->tp_name, (long)op);
			}
			else {
				PyObject *s;
				if (flags & Py_PRINT_RAW)
					s = PyObject_Str(op);
				else
					s = PyObject_Repr(op);
				if (s == NULL)
					ret = -1;
				else {
					ret = PyObject_Print(s, fp,
							     Py_PRINT_RAW);
				}
				Py_XDECREF(s);
			}
		}
		else
			ret = (*op->ob_type->tp_print)(op, fp, flags);
	}
	if (ret == 0) {
		if (ferror(fp)) {
			PyErr_SetFromErrno(PyExc_IOError);
			clearerr(fp);
			ret = -1;
		}
	}
	return ret;
}

PyObject *
PyObject_Repr(v)
	PyObject *v;
{
	if (PyErr_CheckSignals())
		return NULL;
#ifdef USE_STACKCHECK
	if (PyOS_CheckStack()) {
		PyErr_SetString(PyExc_MemoryError, "Stack overflow");
		return NULL;
	}
#endif
	if (v == NULL)
		return PyString_FromString("<NULL>");
	else if (v->ob_type->tp_repr == NULL) {
		char buf[120];
		sprintf(buf, "<%.80s object at %lx>",
			v->ob_type->tp_name, (long)v);
		return PyString_FromString(buf);
	}
	else {
		PyObject *res;
		res = (*v->ob_type->tp_repr)(v);
		if (res == NULL)
			return NULL;
		if (!PyString_Check(res)) {
			PyErr_Format(PyExc_TypeError,
				     "__repr__ returned non-string (type %.200s)",
				     res->ob_type->tp_name);
			Py_DECREF(res);
			return NULL;
		}
		return res;
	}
}

PyObject *
PyObject_Str(v)
	PyObject *v;
{
	PyObject *res;
	
	if (v == NULL)
		return PyString_FromString("<NULL>");
	else if (PyString_Check(v)) {
		Py_INCREF(v);
		return v;
	}
	else if (v->ob_type->tp_str != NULL)
		res = (*v->ob_type->tp_str)(v);
	else {
		PyObject *func;
		if (!PyInstance_Check(v) ||
		    (func = PyObject_GetAttrString(v, "__str__")) == NULL) {
			PyErr_Clear();
			return PyObject_Repr(v);
		}
		res = PyEval_CallObject(func, (PyObject *)NULL);
		Py_DECREF(func);
	}
	if (res == NULL)
		return NULL;
	if (!PyString_Check(res)) {
		PyErr_Format(PyExc_TypeError,
			     "__str__ returned non-string (type %.200s)",
			     res->ob_type->tp_name);
		Py_DECREF(res);
		return NULL;
	}
	return res;
}

static PyObject *
do_cmp(v, w)
	PyObject *v, *w;
{
	long c;
	/* __rcmp__ actually won't be called unless __cmp__ isn't defined,
	   because the check in cmpobject() reverses the objects first.
	   This is intentional -- it makes no sense to define cmp(x,y)
	   different than -cmp(y,x). */
	if (PyInstance_Check(v) || PyInstance_Check(w))
		return PyInstance_DoBinOp(v, w, "__cmp__", "__rcmp__", do_cmp);
	c = PyObject_Compare(v, w);
	if (c && PyErr_Occurred())
		return NULL;
	return PyInt_FromLong(c);
}

PyObject *_PyCompareState_Key;

/* _PyCompareState_nesting is incremented beforing call compare (for
   some types) and decremented on exit.  If the count exceeds the
   nesting limit, enable code to detect circular data structures.
*/
#define NESTING_LIMIT 500
int _PyCompareState_nesting = 0;

static PyObject*
get_inprogress_dict()
{
	PyObject *tstate_dict, *inprogress;

	tstate_dict = PyThreadState_GetDict();
	if (tstate_dict == NULL) {
		PyErr_BadInternalCall();
		return NULL;
	} 
	inprogress = PyDict_GetItem(tstate_dict, _PyCompareState_Key); 
	if (inprogress == NULL) {
		PyErr_Clear();
		inprogress = PyDict_New();
		if (inprogress == NULL)
			return NULL;
		if (PyDict_SetItem(tstate_dict, _PyCompareState_Key,
				   inprogress) == -1) {
		    Py_DECREF(inprogress);
		    return NULL;
		}
	}
	return inprogress;
}

static PyObject *
make_pair(v, w)
	PyObject *v, *w;
{
	PyObject *pair;

	pair = PyTuple_New(2);
	if (pair == NULL) {
		return NULL;
	}
	if ((long)v <= (long)w) {
		PyTuple_SET_ITEM(pair, 0, PyLong_FromVoidPtr((void *)v));
		PyTuple_SET_ITEM(pair, 1, PyLong_FromVoidPtr((void *)w));
	} else {
		PyTuple_SET_ITEM(pair, 0, PyLong_FromVoidPtr((void *)w));
		PyTuple_SET_ITEM(pair, 1, PyLong_FromVoidPtr((void *)v));
	}
	return pair;
}

int
PyObject_Compare(v, w)
	PyObject *v, *w;
{
	PyTypeObject *vtp, *wtp;
	int result;

	if (v == NULL || w == NULL) {
		PyErr_BadInternalCall();
		return -1;
	}
	if (v == w)
		return 0;
	if (PyInstance_Check(v) || PyInstance_Check(w)) {
		PyObject *res;
		int c;
		if (!PyInstance_Check(v))
			return -PyObject_Compare(w, v);
		if (++_PyCompareState_nesting > NESTING_LIMIT) {
			PyObject *inprogress, *pair;

			inprogress = get_inprogress_dict();
			if (inprogress == NULL) {
				return -1;
			}
			pair = make_pair(v, w);
			if (PyDict_GetItem(inprogress, pair)) {
				/* already comparing these objects.  assume
				   they're equal until shown otherwise */
				Py_DECREF(pair);
				--_PyCompareState_nesting;
				return 0;
			}
			if (PyDict_SetItem(inprogress, pair, pair) == -1) {
				return -1;
			}
			res = do_cmp(v, w);
			_PyCompareState_nesting--;
			/* XXX DelItem shouldn't fail */
			PyDict_DelItem(inprogress, pair);
			Py_DECREF(pair);
		} else {
			res = do_cmp(v, w);
		}
		if (res == NULL)
			return -1;
		if (!PyInt_Check(res)) {
			Py_DECREF(res);
			PyErr_SetString(PyExc_TypeError,
					"comparison did not return an int");
			return -1;
		}
		c = PyInt_AsLong(res);
		Py_DECREF(res);
		return (c < 0) ? -1 : (c > 0) ? 1 : 0;	
	}
	if ((vtp = v->ob_type) != (wtp = w->ob_type)) {
		char *vname = vtp->tp_name;
		char *wname = wtp->tp_name;
		if (vtp->tp_as_number != NULL && wtp->tp_as_number != NULL) {
			int err;
			err = PyNumber_CoerceEx(&v, &w);
			if (err < 0)
				return -1;
			else if (err == 0) {
				int cmp;
				vtp = v->ob_type;
				if (vtp->tp_compare == NULL)
					cmp = (v < w) ? -1 : 1;
				else
					cmp = (*vtp->tp_compare)(v, w);
				Py_DECREF(v);
				Py_DECREF(w);
				return cmp;
			}
		}
		else if (PyUnicode_Check(v) || PyUnicode_Check(w)) {
			int result = PyUnicode_Compare(v, w);
			if (result == -1 && PyErr_Occurred() && 
			    PyErr_ExceptionMatches(PyExc_TypeError))
				/* TypeErrors are ignored: if Unicode coercion
				fails due to one of the arguments not
			 	having the right type, we continue as
				defined by the coercion protocol (see
				above). Luckily, decoding errors are
				reported as ValueErrors and are not masked
				by this technique. */
				PyErr_Clear();
			else
				return result;
		}
		else if (vtp->tp_as_number != NULL)
			vname = "";
		else if (wtp->tp_as_number != NULL)
			wname = "";
		/* Numerical types compare smaller than all other types */
		return strcmp(vname, wname);
	}
	if (vtp->tp_compare == NULL) {
		return (v < w) ? -1 : 1;
	}
	if (++_PyCompareState_nesting > NESTING_LIMIT
	    && (vtp->tp_as_mapping 
		|| (vtp->tp_as_sequence && !PyString_Check(v)))) {
		PyObject *inprogress, *pair;

		inprogress = get_inprogress_dict();
		if (inprogress == NULL) {
			return -1;
		}
		pair = make_pair(v, w);
		if (PyDict_GetItem(inprogress, pair)) {
			/* already comparing these objects.  assume
			   they're equal until shown otherwise */
			_PyCompareState_nesting--;
			Py_DECREF(pair);
			return 0;
		}
		if (PyDict_SetItem(inprogress, pair, pair) == -1) {
			return -1;
		}
		result = (*vtp->tp_compare)(v, w);
		_PyCompareState_nesting--;
		PyDict_DelItem(inprogress, pair); /* XXX shouldn't fail */
		Py_DECREF(pair);
	} else {
		result = (*vtp->tp_compare)(v, w);
	}
	return result;
}

long
PyObject_Hash(v)
	PyObject *v;
{
	PyTypeObject *tp = v->ob_type;
	if (tp->tp_hash != NULL)
		return (*tp->tp_hash)(v);
	if (tp->tp_compare == NULL)
		return (long) v; /* Use address as hash value */
	/* If there's a cmp but no hash defined, the object can't be hashed */
	PyErr_SetString(PyExc_TypeError, "unhashable type");
	return -1;
}

PyObject *
PyObject_GetAttrString(v, name)
	PyObject *v;
	char *name;
{
	if (v->ob_type->tp_getattro != NULL) {
		PyObject *w, *res;
		w = PyString_InternFromString(name);
		if (w == NULL)
			return NULL;
		res = (*v->ob_type->tp_getattro)(v, w);
		Py_XDECREF(w);
		return res;
	}

	if (v->ob_type->tp_getattr == NULL) {
		PyErr_Format(PyExc_AttributeError,
			     "'%.50s' object has no attribute '%.400s'",
			     v->ob_type->tp_name,
			     name);
		return NULL;
	}
	else {
		return (*v->ob_type->tp_getattr)(v, name);
	}
}

int
PyObject_HasAttrString(v, name)
	PyObject *v;
	char *name;
{
	PyObject *res = PyObject_GetAttrString(v, name);
	if (res != NULL) {
		Py_DECREF(res);
		return 1;
	}
	PyErr_Clear();
	return 0;
}

int
PyObject_SetAttrString(v, name, w)
	PyObject *v;
	char *name;
	PyObject *w;
{
	if (v->ob_type->tp_setattro != NULL) {
		PyObject *s;
		int res;
		s = PyString_InternFromString(name);
		if (s == NULL)
			return -1;
		res = (*v->ob_type->tp_setattro)(v, s, w);
		Py_XDECREF(s);
		return res;
	}

	if (v->ob_type->tp_setattr == NULL) {
		if (v->ob_type->tp_getattr == NULL)
			PyErr_SetString(PyExc_TypeError,
				   "attribute-less object (assign or del)");
		else
			PyErr_SetString(PyExc_TypeError,
				   "object has read-only attributes");
		return -1;
	}
	else {
		return (*v->ob_type->tp_setattr)(v, name, w);
	}
}

PyObject *
PyObject_GetAttr(v, name)
	PyObject *v;
	PyObject *name;
{
	if (v->ob_type->tp_getattro != NULL)
		return (*v->ob_type->tp_getattro)(v, name);
	else
		return PyObject_GetAttrString(v, PyString_AsString(name));
}

int
PyObject_HasAttr(v, name)
	PyObject *v;
	PyObject *name;
{
	PyObject *res = PyObject_GetAttr(v, name);
	if (res != NULL) {
		Py_DECREF(res);
		return 1;
	}
	PyErr_Clear();
	return 0;
}

int
PyObject_SetAttr(v, name, value)
	PyObject *v;
	PyObject *name;
	PyObject *value;
{
	int err;
	Py_INCREF(name);
	PyString_InternInPlace(&name);
	if (v->ob_type->tp_setattro != NULL)
		err = (*v->ob_type->tp_setattro)(v, name, value);
	else
		err = PyObject_SetAttrString(
			v, PyString_AsString(name), value);
	Py_DECREF(name);
	return err;
}

/* Test a value used as condition, e.g., in a for or if statement.
   Return -1 if an error occurred */

int
PyObject_IsTrue(v)
	PyObject *v;
{
	int res;
	if (v == Py_None)
		res = 0;
	else if (v->ob_type->tp_as_number != NULL &&
		 v->ob_type->tp_as_number->nb_nonzero != NULL)
		res = (*v->ob_type->tp_as_number->nb_nonzero)(v);
	else if (v->ob_type->tp_as_mapping != NULL &&
		 v->ob_type->tp_as_mapping->mp_length != NULL)
		res = (*v->ob_type->tp_as_mapping->mp_length)(v);
	else if (v->ob_type->tp_as_sequence != NULL &&
		 v->ob_type->tp_as_sequence->sq_length != NULL)
		res = (*v->ob_type->tp_as_sequence->sq_length)(v);
	else
		res = 1;
	if (res > 0)
		res = 1;
	return res;
}

/* equivalent of 'not v' 
   Return -1 if an error occurred */

int
PyObject_Not(v)
	PyObject *v;
{
	int res;
	res = PyObject_IsTrue(v);
	if (res < 0)
		return res;
	return res == 0;
}

/* Coerce two numeric types to the "larger" one.
   Increment the reference count on each argument.
   Return -1 and raise an exception if no coercion is possible
   (and then no reference count is incremented).
*/

int
PyNumber_CoerceEx(pv, pw)
	PyObject **pv, **pw;
{
	register PyObject *v = *pv;
	register PyObject *w = *pw;
	int res;

	if (v->ob_type == w->ob_type && !PyInstance_Check(v)) {
		Py_INCREF(v);
		Py_INCREF(w);
		return 0;
	}
	if (v->ob_type->tp_as_number && v->ob_type->tp_as_number->nb_coerce) {
		res = (*v->ob_type->tp_as_number->nb_coerce)(pv, pw);
		if (res <= 0)
			return res;
	}
	if (w->ob_type->tp_as_number && w->ob_type->tp_as_number->nb_coerce) {
		res = (*w->ob_type->tp_as_number->nb_coerce)(pw, pv);
		if (res <= 0)
			return res;
	}
	return 1;
}

int
PyNumber_Coerce(pv, pw)
	PyObject **pv, **pw;
{
	int err = PyNumber_CoerceEx(pv, pw);
	if (err <= 0)
		return err;
	PyErr_SetString(PyExc_TypeError, "number coercion failed");
	return -1;
}


/* Test whether an object can be called */

int
PyCallable_Check(x)
	PyObject *x;
{
	if (x == NULL)
		return 0;
	if (x->ob_type->tp_call != NULL ||
	    PyFunction_Check(x) ||
	    PyMethod_Check(x) ||
	    PyCFunction_Check(x) ||
	    PyClass_Check(x))
		return 1;
	if (PyInstance_Check(x)) {
		PyObject *call = PyObject_GetAttrString(x, "__call__");
		if (call == NULL) {
			PyErr_Clear();
			return 0;
		}
		/* Could test recursively but don't, for fear of endless
		   recursion if some joker sets self.__call__ = self */
		Py_DECREF(call);
		return 1;
	}
	return 0;
}


/*
NoObject is usable as a non-NULL undefined value, used by the macro None.
There is (and should be!) no way to create other objects of this type,
so there is exactly one (which is indestructible, by the way).
*/

/* ARGSUSED */
static PyObject *
none_repr(op)
	PyObject *op;
{
	return PyString_FromString("None");
}

static PyTypeObject PyNothing_Type = {
	PyObject_HEAD_INIT(&PyType_Type)
	0,
	"None",
	0,
	0,
	0,		/*tp_dealloc*/ /*never called*/
	0,		/*tp_print*/
	0,		/*tp_getattr*/
	0,		/*tp_setattr*/
	0,		/*tp_compare*/
	(reprfunc)none_repr, /*tp_repr*/
	0,		/*tp_as_number*/
	0,		/*tp_as_sequence*/
	0,		/*tp_as_mapping*/
	0,		/*tp_hash */
};

PyObject _Py_NoneStruct = {
	PyObject_HEAD_INIT(&PyNothing_Type)
};


#ifdef Py_TRACE_REFS

static PyObject refchain = {&refchain, &refchain};

void
_Py_ResetReferences()
{
	refchain._ob_prev = refchain._ob_next = &refchain;
	_Py_RefTotal = 0;
}

void
_Py_NewReference(op)
	PyObject *op;
{
	_Py_RefTotal++;
	op->ob_refcnt = 1;
	op->_ob_next = refchain._ob_next;
	op->_ob_prev = &refchain;
	refchain._ob_next->_ob_prev = op;
	refchain._ob_next = op;
#ifdef COUNT_ALLOCS
	inc_count(op->ob_type);
#endif
}

void
_Py_ForgetReference(op)
	register PyObject *op;
{
#ifdef SLOW_UNREF_CHECK
        register PyObject *p;
#endif
	if (op->ob_refcnt < 0)
		Py_FatalError("UNREF negative refcnt");
	if (op == &refchain ||
	    op->_ob_prev->_ob_next != op || op->_ob_next->_ob_prev != op)
		Py_FatalError("UNREF invalid object");
#ifdef SLOW_UNREF_CHECK
	for (p = refchain._ob_next; p != &refchain; p = p->_ob_next) {
		if (p == op)
			break;
	}
	if (p == &refchain) /* Not found */
		Py_FatalError("UNREF unknown object");
#endif
	op->_ob_next->_ob_prev = op->_ob_prev;
	op->_ob_prev->_ob_next = op->_ob_next;
	op->_ob_next = op->_ob_prev = NULL;
#ifdef COUNT_ALLOCS
	op->ob_type->tp_free++;
#endif
}

void
_Py_Dealloc(op)
	PyObject *op;
{
	destructor dealloc = op->ob_type->tp_dealloc;
	_Py_ForgetReference(op);
	if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL-1)
		op->ob_type = NULL;
	(*dealloc)(op);
}

void
_Py_PrintReferences(fp)
	FILE *fp;
{
	PyObject *op;
	fprintf(fp, "Remaining objects:\n");
	for (op = refchain._ob_next; op != &refchain; op = op->_ob_next) {
		fprintf(fp, "[%d] ", op->ob_refcnt);
		if (PyObject_Print(op, fp, 0) != 0)
			PyErr_Clear();
		putc('\n', fp);
	}
}

PyObject *
_Py_GetObjects(self, args)
	PyObject *self;
	PyObject *args;
{
	int i, n;
	PyObject *t = NULL;
	PyObject *res, *op;

	if (!PyArg_ParseTuple(args, "i|O", &n, &t))
		return NULL;
	op = refchain._ob_next;
	res = PyList_New(0);
	if (res == NULL)
		return NULL;
	for (i = 0; (n == 0 || i < n) && op != &refchain; i++) {
		while (op == self || op == args || op == res || op == t ||
		       t != NULL && op->ob_type != (PyTypeObject *) t) {
			op = op->_ob_next;
			if (op == &refchain)
				return res;
		}
		if (PyList_Append(res, op) < 0) {
			Py_DECREF(res);
			return NULL;
		}
		op = op->_ob_next;
	}
	return res;
}

#endif


/* Hack to force loading of cobject.o */
PyTypeObject *_Py_cobject_hack = &PyCObject_Type;


/* Hack to force loading of abstract.o */
int (*_Py_abstract_hack) Py_FPROTO((PyObject *)) = &PyObject_Length;


/* Malloc wrappers (see mymalloc.h) */

/* The Py_{Malloc,Realloc} wrappers call PyErr_NoMemory() on failure */

ANY *
Py_Malloc(nbytes)
	size_t nbytes;
{
	ANY *p;
#if _PyMem_EXTRA > 0
	if (nbytes == 0)
		nbytes = _PyMem_EXTRA;
#endif
	p = malloc(nbytes);
	if (p != NULL)
		return p;
	else {
		PyErr_NoMemory();
		return NULL;
	}
}

ANY *
Py_Realloc(p, nbytes)
	ANY *p;
	size_t nbytes;
{
#if _PyMem_EXTRA > 0
	if (nbytes == 0)
		nbytes = _PyMem_EXTRA;
#endif
	p = realloc(p, nbytes);
	if (p != NULL)
		return p;
	else {
		PyErr_NoMemory();
		return NULL;
	}
}

void
Py_Free(p)
	ANY *p;
{
	free(p);
}

/* The PyMem_{Malloc,Realloc} wrappers don't call anything on failure */

ANY *
PyMem_Malloc(nbytes)
	size_t nbytes;
{
#if _PyMem_EXTRA > 0
	if (nbytes == 0)
		nbytes = _PyMem_EXTRA;
#endif
	return malloc(nbytes);
}

ANY *
PyMem_Realloc(p, nbytes)
	ANY *p;
	size_t nbytes;
{
#if _PyMem_EXTRA > 0
	if (nbytes == 0)
		nbytes = _PyMem_EXTRA;
#endif
	return realloc(p, nbytes);
}

void
PyMem_Free(p)
	ANY *p;
{
	free(p);
}


/* These methods are used to control infinite recursion in repr, str, print,
   etc.  Container objects that may recursively contain themselves,
   e.g. builtin dictionaries and lists, should used Py_ReprEnter() and
   Py_ReprLeave() to avoid infinite recursion.

   Py_ReprEnter() returns 0 the first time it is called for a particular
   object and 1 every time thereafter.  It returns -1 if an exception
   occurred.  Py_ReprLeave() has no return value.

   See dictobject.c and listobject.c for examples of use.
*/

#define KEY "Py_Repr"

int
Py_ReprEnter(obj)
	PyObject *obj;
{
	PyObject *dict;
	PyObject *list;
	int i;

	dict = PyThreadState_GetDict();
	if (dict == NULL)
		return -1;
	list = PyDict_GetItemString(dict, KEY);
	if (list == NULL) {
		list = PyList_New(0);
		if (list == NULL)
			return -1;
		if (PyDict_SetItemString(dict, KEY, list) < 0)
			return -1;
		Py_DECREF(list);
	}
	i = PyList_GET_SIZE(list);
	while (--i >= 0) {
		if (PyList_GET_ITEM(list, i) == obj)
			return 1;
	}
	PyList_Append(list, obj);
	return 0;
}

void
Py_ReprLeave(obj)
	PyObject *obj;
{
	PyObject *dict;
	PyObject *list;
	int i;

	dict = PyThreadState_GetDict();
	if (dict == NULL)
		return;
	list = PyDict_GetItemString(dict, KEY);
	if (list == NULL || !PyList_Check(list))
		return;
	i = PyList_GET_SIZE(list);
	/* Count backwards because we always expect obj to be list[-1] */
	while (--i >= 0) {
		if (PyList_GET_ITEM(list, i) == obj) {
			PyList_SetSlice(list, i, i + 1, NULL);
			break;
		}
	}
}

/*
  trashcan
  CT 2k0130
  non-recursively destroy nested objects

  CT 2k0223
  everything is now done in a macro.

  CT 2k0305
  modified to use functions, after Tim Peter's suggestion.

  CT 2k0309
  modified to restore a possible error.

  CT 2k0325
  added better safe than sorry check for threadstate

  CT 2k0422
  complete rewrite. We now build a chain via ob_type
  and save the limited number of types in ob_refcnt.
  This is perfect since we don't need any memory.
  A patch for free-threading would need just a lock.
*/

#define Py_TRASHCAN_TUPLE       1
#define Py_TRASHCAN_LIST        2
#define Py_TRASHCAN_DICT        3
#define Py_TRASHCAN_FRAME       4
#define Py_TRASHCAN_TRACEBACK   5
/* extend here if other objects want protection */

int _PyTrash_delete_nesting = 0;

PyObject * _PyTrash_delete_later = NULL;

void
_PyTrash_deposit_object(op)
	PyObject *op;
{
	int typecode;
	PyObject *hold = _PyTrash_delete_later;

	if (PyTuple_Check(op))
		typecode = Py_TRASHCAN_TUPLE;
	else if (PyList_Check(op))
		typecode = Py_TRASHCAN_LIST;
	else if (PyDict_Check(op))
		typecode = Py_TRASHCAN_DICT;
	else if (PyFrame_Check(op))
		typecode = Py_TRASHCAN_FRAME;
	else if (PyTraceBack_Check(op))
		typecode = Py_TRASHCAN_TRACEBACK;
	op->ob_refcnt = typecode;

	op->ob_type = (PyTypeObject*)_PyTrash_delete_later;
	_PyTrash_delete_later = op;
}

void
_PyTrash_destroy_chain()
{
	while (_PyTrash_delete_later) {
		PyObject *shredder = _PyTrash_delete_later;
		_PyTrash_delete_later = (PyObject*) shredder->ob_type;

		switch (shredder->ob_refcnt) {
		case Py_TRASHCAN_TUPLE:
			shredder->ob_type = &PyTuple_Type;
			break;
		case Py_TRASHCAN_LIST:
			shredder->ob_type = &PyList_Type;
			break;
		case Py_TRASHCAN_DICT:
			shredder->ob_type = &PyDict_Type;
			break;
		case Py_TRASHCAN_FRAME:
			shredder->ob_type = &PyFrame_Type;
			break;
		case Py_TRASHCAN_TRACEBACK:
			shredder->ob_type = &PyTraceBack_Type;
			break;
		}
		_Py_NewReference(shredder);

		++_PyTrash_delete_nesting;
		Py_DECREF(shredder);
		--_PyTrash_delete_nesting;
	}
}