cpython/Objects/object.c

/***********************************************************
Copyright (c) 2000, BeOpen.com.
Copyright (c) 1995-2000, Corporation for National Research Initiatives.
Copyright (c) 1990-1995, Stichting Mathematisch Centrum.
All rights reserved.

See the file "Misc/COPYRIGHT" for information on usage and
redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES.
******************************************************************/

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

#include "Python.h"

#ifdef macintosh
#include "macglue.h"
#endif

/* 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(void)
{
	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(void)
{
	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(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

PyObject *
PyObject_Init(PyObject *op, PyTypeObject *tp)
{
	if (op == NULL) {
		PyErr_SetString(PyExc_SystemError,
				"NULL object passed to PyObject_Init");
		return op;
  	}
#ifdef WITH_CYCLE_GC
	if (PyType_IS_GC(tp))
		op = (PyObject *) PyObject_FROM_GC(op);
#endif
	/* Any changes should be reflected in PyObject_INIT (objimpl.h) */
	op->ob_type = tp;
	_Py_NewReference(op);
	return op;
}

PyVarObject *
PyObject_InitVar(PyVarObject *op, PyTypeObject *tp, int size)
{
	if (op == NULL) {
		PyErr_SetString(PyExc_SystemError,
				"NULL object passed to PyObject_InitVar");
		return op;
	}
#ifdef WITH_CYCLE_GC
	if (PyType_IS_GC(tp))
		op = (PyVarObject *) PyObject_FROM_GC(op);
#endif
	/* Any changes should be reflected in PyObject_INIT_VAR */
	op->ob_size = size;
	op->ob_type = tp;
	_Py_NewReference((PyObject *)op);
	return op;
}

PyObject *
_PyObject_New(PyTypeObject *tp)
{
	PyObject *op;
	op = (PyObject *) PyObject_MALLOC(_PyObject_SIZE(tp));
	if (op == NULL)
		return PyErr_NoMemory();
#ifdef WITH_CYCLE_GC
	if (PyType_IS_GC(tp))
		op = (PyObject *) PyObject_FROM_GC(op);
#endif
	return PyObject_INIT(op, tp);
}

PyVarObject *
_PyObject_NewVar(PyTypeObject *tp, int size)
{
	PyVarObject *op;
	op = (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE(tp, size));
	if (op == NULL)
		return (PyVarObject *)PyErr_NoMemory();
#ifdef WITH_CYCLE_GC
	if (PyType_IS_GC(tp))
		op = (PyVarObject *) PyObject_FROM_GC(op);
#endif
	return PyObject_INIT_VAR(op, tp, size);
}

void
_PyObject_Del(PyObject *op)
{
#ifdef WITH_CYCLE_GC
	if (op && PyType_IS_GC(op->ob_type)) {
		op = (PyObject *) PyObject_AS_GC(op);
	}
#endif
	PyObject_FREE(op);
}

#ifndef WITH_CYCLE_GC
/* extension modules might need these */
void _PyGC_Insert(PyObject *op) { }
void _PyGC_Remove(PyObject *op) { }
#endif

int
PyObject_Print(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 %p>",
				op->ob_refcnt, op);
		else if (op->ob_type->tp_print == NULL) {
			if (op->ob_type->tp_repr == NULL) {
				fprintf(fp, "<%s object at %p>",
					op->ob_type->tp_name, 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(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 %p>",
			v->ob_type->tp_name, v);
		return PyString_FromString(buf);
	}
	else {
		PyObject *res;
		res = (*v->ob_type->tp_repr)(v);
		if (res == NULL)
			return NULL;
		if (PyUnicode_Check(res)) {
			PyObject* str;
			str = PyUnicode_AsUnicodeEscapeString(res);
			Py_DECREF(res);
			if (str)
				res = str;
			else
				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(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 (PyUnicode_Check(res)) {
		PyObject* str;
		str = PyUnicode_AsEncodedString(res, NULL, NULL);
		Py_DECREF(res);
		if (str)
			res = str;
		else
		    	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(PyObject *v, PyObject *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 before calling 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(void)
{
	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) {
		inprogress = PyDict_New();
		if (inprogress == NULL)
			return NULL;
		if (PyDict_SetItem(tstate_dict, _PyCompareState_Key,
				   inprogress) == -1) {
		    Py_DECREF(inprogress);
		    return NULL;
		}
		Py_DECREF(inprogress);
	}
	return inprogress;
}

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

	pair = PyTuple_New(2);
	if (pair == NULL) {
		return NULL;
	}
	if (v <= 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(PyObject *v, PyObject *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);
		_PyCompareState_nesting++;
		if (_PyCompareState_nesting > NESTING_LIMIT) {
			PyObject *inprogress, *pair;

			inprogress = get_inprogress_dict();
			if (inprogress == NULL) {
				_PyCompareState_nesting--;
				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) {
				_PyCompareState_nesting--;
				return -1;
			}
			res = do_cmp(v, w);
			/* XXX DelItem shouldn't fail */
			PyDict_DelItem(inprogress, pair);
			Py_DECREF(pair);
		} else {
			res = do_cmp(v, w);
		}
		_PyCompareState_nesting--;
		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;
	}
	_PyCompareState_nesting++;
	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) {
			_PyCompareState_nesting--;
			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) {
			_PyCompareState_nesting--;
			return -1;
		}
		result = (*vtp->tp_compare)(v, w);
		PyDict_DelItem(inprogress, pair); /* XXX shouldn't fail */
		Py_DECREF(pair);
	} else {
		result = (*vtp->tp_compare)(v, w);
	}
	_PyCompareState_nesting--;
	return result;
}


/* Set of hash utility functions to help maintaining the invariant that
	iff a==b then hash(a)==hash(b)

   All the utility functions (_Py_Hash*()) return "-1" to signify an error.
*/

long
_Py_HashDouble(double v)
{
	/* Use frexp to get at the bits in the double.
	 * Since the VAX D double format has 56 mantissa bits, which is the
	 * most of any double format in use, each of these parts may have as
	 * many as (but no more than) 56 significant bits.
	 * So, assuming sizeof(long) >= 4, each part can be broken into two longs;
	 * frexp and multiplication are used to do that.
	 * Also, since the Cray double format has 15 exponent bits, which is the
	 * most of any double format in use, shifting the exponent field left by
	 * 15 won't overflow a long (again assuming sizeof(long) >= 4).
	 */
    int expo;
    long hipart;

    v = frexp(v, &expo);
    v = v * 2147483648.0; /* 2**31 */
    hipart = (long)v; /* Take the top 32 bits */
	v = (v - (double)hipart) * 2147483648.0; /* Get the next 32 bits */

    return hipart + (long)v + (expo << 15); /* Combine everything */
}

long
_Py_HashPointer(void *p)
{
#if SIZEOF_LONG >= SIZEOF_VOID_P
	return (long)p;
#else
	/* convert to a Python long and hash that */
	PyObject* longobj;
	long x;
	
	if ((longobj = PyLong_FromVoidPtr(p)) == NULL) {
		x = -1;
		goto finally;
	}
	x = PyObject_Hash(longobj);
	
finally:
	Py_XDECREF(longobj);
	return x;
#endif
}


long
PyObject_Hash(PyObject *v)
{
	PyTypeObject *tp = v->ob_type;
	if (tp->tp_hash != NULL)
		return (*tp->tp_hash)(v);
	if (tp->tp_compare == NULL) {
		return _Py_HashPointer(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(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(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(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(PyObject *v, PyObject *name)
{
	if (v->ob_type->tp_getattro != NULL)
		return (*v->ob_type->tp_getattro)(v, name);

	if (!PyString_Check(name)) {
		PyErr_SetString(PyExc_TypeError,
				"attribute name must be string");
		return NULL;
	}
	return PyObject_GetAttrString(v, PyString_AS_STRING(name));
}

int
PyObject_HasAttr(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(PyObject *v, PyObject *name, PyObject *value)
{
	int err;
	Py_INCREF(name);
	if (PyString_Check(name))
		PyString_InternInPlace(&name);
	if (v->ob_type->tp_setattro != NULL)
		err = (*v->ob_type->tp_setattro)(v, name, value);
	else if (PyString_Check(name)) {
		err = PyObject_SetAttrString(
			v, PyString_AS_STRING(name), value);
	}
	else {
		PyErr_SetString(PyExc_TypeError,
				"attribute name must be string");
		err = -1;
	}
	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(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(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(PyObject **pv, PyObject **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(PyObject **pv, PyObject **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(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(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(void)
{
	refchain._ob_prev = refchain._ob_next = &refchain;
	_Py_RefTotal = 0;
}

void
_Py_NewReference(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(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(PyObject *op)
{
	destructor dealloc = op->ob_type->tp_dealloc;
	_Py_ForgetReference(op);
#ifndef WITH_CYCLE_GC
	if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL-1)
		op->ob_type = NULL;
#endif
	(*dealloc)(op);
}

void
_Py_PrintReferences(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(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)(PyObject *) = &PyObject_Size;


/* Python's malloc wrappers (see mymalloc.h) */

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

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

void
PyMem_Free(void *p)
{
	PyMem_FREE(p);
}


/* Python's object malloc wrappers (see objimpl.h) */

void *
PyObject_Malloc(size_t nbytes)
{
	return PyObject_MALLOC(nbytes);
}

void *
PyObject_Realloc(void *p, size_t nbytes)
{
	return PyObject_REALLOC(p, nbytes);
}

void
PyObject_Free(void *p)
{
	PyObject_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(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(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(PyObject *op)
{
	int typecode;

	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;
	else /* We have a bug here -- those are the only types in GC */ {
		Py_FatalError("Type not supported in GC -- internal bug");
		return; /* pacify compiler -- execution never here */
	}
	op->ob_refcnt = typecode;

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

void
_PyTrash_destroy_chain(void)
{
	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;
	}
}