Objects/abstract.c

/* Abstract Object Interface (many thanks to Jim Fulton) */

#include "Python.h"
#include <ctype.h>
#include "structmember.h" /* we need the offsetof() macro from there */
#include "longintrepr.h"



/* Shorthands to return certain errors */

static PyObject *
type_error(const char *msg, PyObject *obj)
{
	PyErr_Format(PyExc_TypeError, msg, obj->ob_type->tp_name);
	return NULL;
}

static PyObject *
null_error(void)
{
	if (!PyErr_Occurred())
		PyErr_SetString(PyExc_SystemError,
				"null argument to internal routine");
	return NULL;
}

/* Operations on any object */

PyObject *
PyObject_Type(PyObject *o)
{
	PyObject *v;

	if (o == NULL)
		return null_error();
	v = (PyObject *)o->ob_type;
	Py_INCREF(v);
	return v;
}

Py_ssize_t
PyObject_Size(PyObject *o)
{
	PySequenceMethods *m;

	if (o == NULL) {
		null_error();
		return -1;
	}

	m = o->ob_type->tp_as_sequence;
	if (m && m->sq_length)
		return m->sq_length(o);

	return PyMapping_Size(o);
}

#undef PyObject_Length
Py_ssize_t
PyObject_Length(PyObject *o)
{
	return PyObject_Size(o);
}
#define PyObject_Length PyObject_Size


/* The length hint function returns a non-negative value from o.__len__()
   or o.__length_hint__().  If those methods aren't found or return a negative
   value, then the defaultvalue is returned.  If one of the calls fails,
   this function returns -1.
*/

Py_ssize_t
_PyObject_LengthHint(PyObject *o, Py_ssize_t defaultvalue)
{
	static PyObject *hintstrobj = NULL;
	PyObject *ro, *hintmeth;
	Py_ssize_t rv;

	/* try o.__len__() */
	rv = PyObject_Size(o);
	if (rv >= 0)
		return rv;
	if (PyErr_Occurred()) {
		if (!PyErr_ExceptionMatches(PyExc_TypeError))
			return -1;
		PyErr_Clear();
	}

	/* try o.__length_hint__() */
        hintmeth = _PyObject_LookupSpecial(o, "__length_hint__", &hintstrobj);
	if (hintmeth == NULL) {
		if (PyErr_Occurred())
			return -1;
		else
			return defaultvalue;
	}
	ro = PyObject_CallFunctionObjArgs(hintmeth, NULL);
	Py_DECREF(hintmeth);
	if (ro == NULL) {
		if (!PyErr_ExceptionMatches(PyExc_TypeError))
			return -1;
		PyErr_Clear();
		return defaultvalue;
	}
	rv = PyLong_Check(ro) ? PyLong_AsSsize_t(ro) : defaultvalue;
	Py_DECREF(ro);
	return rv;
}

PyObject *
PyObject_GetItem(PyObject *o, PyObject *key)
{
	PyMappingMethods *m;

	if (o == NULL || key == NULL)
		return null_error();

	m = o->ob_type->tp_as_mapping;
	if (m && m->mp_subscript)
		return m->mp_subscript(o, key);

	if (o->ob_type->tp_as_sequence) {
		if (PyIndex_Check(key)) {
			Py_ssize_t key_value;
			key_value = PyNumber_AsSsize_t(key, PyExc_IndexError);
			if (key_value == -1 && PyErr_Occurred())
				return NULL;
			return PySequence_GetItem(o, key_value);
		}
		else if (o->ob_type->tp_as_sequence->sq_item)
			return type_error("sequence index must "
					  "be integer, not '%.200s'", key);
	}

	return type_error("'%.200s' object is not subscriptable", o);
}

int
PyObject_SetItem(PyObject *o, PyObject *key, PyObject *value)
{
	PyMappingMethods *m;

	if (o == NULL || key == NULL || value == NULL) {
		null_error();
		return -1;
	}
	m = o->ob_type->tp_as_mapping;
	if (m && m->mp_ass_subscript)
		return m->mp_ass_subscript(o, key, value);

	if (o->ob_type->tp_as_sequence) {
		if (PyIndex_Check(key)) {
			Py_ssize_t key_value;
			key_value = PyNumber_AsSsize_t(key, PyExc_IndexError);
			if (key_value == -1 && PyErr_Occurred())
				return -1;
			return PySequence_SetItem(o, key_value, value);
		}
		else if (o->ob_type->tp_as_sequence->sq_ass_item) {
			type_error("sequence index must be "
				   "integer, not '%.200s'", key);
			return -1;
		}
	}

	type_error("'%.200s' object does not support item assignment", o);
	return -1;
}

int
PyObject_DelItem(PyObject *o, PyObject *key)
{
	PyMappingMethods *m;

	if (o == NULL || key == NULL) {
		null_error();
		return -1;
	}
	m = o->ob_type->tp_as_mapping;
	if (m && m->mp_ass_subscript)
		return m->mp_ass_subscript(o, key, (PyObject*)NULL);

	if (o->ob_type->tp_as_sequence) {
		if (PyIndex_Check(key)) {
			Py_ssize_t key_value;
			key_value = PyNumber_AsSsize_t(key, PyExc_IndexError);
			if (key_value == -1 && PyErr_Occurred())
				return -1;
			return PySequence_DelItem(o, key_value);
		}
		else if (o->ob_type->tp_as_sequence->sq_ass_item) {
			type_error("sequence index must be "
				   "integer, not '%.200s'", key);
			return -1;
		}
	}

	type_error("'%.200s' object does not support item deletion", o);
	return -1;
}

int
PyObject_DelItemString(PyObject *o, char *key)
{
	PyObject *okey;
	int ret;

	if (o == NULL || key == NULL) {
		null_error();
		return -1;
	}
	okey = PyUnicode_FromString(key);
	if (okey == NULL)
		return -1;
	ret = PyObject_DelItem(o, okey);
	Py_DECREF(okey);
	return ret;
}

/* We release the buffer right after use of this function which could
   cause issues later on.  Don't use these functions in new code.
 */
int
PyObject_AsCharBuffer(PyObject *obj,
		      const char **buffer,
		      Py_ssize_t *buffer_len)
{
	PyBufferProcs *pb;
	Py_buffer view;

	if (obj == NULL || buffer == NULL || buffer_len == NULL) {
		null_error();
		return -1;
	}
	pb = obj->ob_type->tp_as_buffer;
	if (pb == NULL || pb->bf_getbuffer == NULL) {
		PyErr_SetString(PyExc_TypeError,
				"expected an object with the buffer interface");
		return -1;
	}
	if ((*pb->bf_getbuffer)(obj, &view, PyBUF_SIMPLE)) return -1;

	*buffer = view.buf;
	*buffer_len = view.len;
	if (pb->bf_releasebuffer != NULL)
		(*pb->bf_releasebuffer)(obj, &view);
	Py_XDECREF(view.obj);
	return 0;
}

int
PyObject_CheckReadBuffer(PyObject *obj)
{
	PyBufferProcs *pb = obj->ob_type->tp_as_buffer;
	Py_buffer view;

	if (pb == NULL ||
	    pb->bf_getbuffer == NULL)
		return 0;
	if ((*pb->bf_getbuffer)(obj, &view, PyBUF_SIMPLE) == -1) {
		PyErr_Clear();
		return 0;
	}
	PyBuffer_Release(&view);
	return 1;
}

int PyObject_AsReadBuffer(PyObject *obj,
			  const void **buffer,
			  Py_ssize_t *buffer_len)
{
	PyBufferProcs *pb;
	Py_buffer view;

	if (obj == NULL || buffer == NULL || buffer_len == NULL) {
		null_error();
		return -1;
	}
	pb = obj->ob_type->tp_as_buffer;
	if (pb == NULL ||
	    pb->bf_getbuffer == NULL) {
		PyErr_SetString(PyExc_TypeError,
				"expected an object with a buffer interface");
		return -1;
	}

	if ((*pb->bf_getbuffer)(obj, &view, PyBUF_SIMPLE)) return -1;

	*buffer = view.buf;
	*buffer_len = view.len;
	if (pb->bf_releasebuffer != NULL)
		(*pb->bf_releasebuffer)(obj, &view);
	Py_XDECREF(view.obj);
	return 0;
}

int PyObject_AsWriteBuffer(PyObject *obj,
			   void **buffer,
			   Py_ssize_t *buffer_len)
{
	PyBufferProcs *pb;
	Py_buffer view;

	if (obj == NULL || buffer == NULL || buffer_len == NULL) {
		null_error();
		return -1;
	}
	pb = obj->ob_type->tp_as_buffer;
	if (pb == NULL ||
	    pb->bf_getbuffer == NULL ||
	    ((*pb->bf_getbuffer)(obj, &view, PyBUF_WRITABLE) != 0)) {
		PyErr_SetString(PyExc_TypeError,
				"expected an object with a writable buffer interface");
		return -1;
	}

	*buffer = view.buf;
	*buffer_len = view.len;
	if (pb->bf_releasebuffer != NULL)
		(*pb->bf_releasebuffer)(obj, &view);
	Py_XDECREF(view.obj);
	return 0;
}

/* Buffer C-API for Python 3.0 */

int
PyObject_GetBuffer(PyObject *obj, Py_buffer *view, int flags)
{
	if (!PyObject_CheckBuffer(obj)) {
		PyErr_Format(PyExc_TypeError,
                             "'%100s' does not support the buffer interface",
                             Py_TYPE(obj)->tp_name);
		return -1;
	}
	return (*(obj->ob_type->tp_as_buffer->bf_getbuffer))(obj, view, flags);
}

static int
_IsFortranContiguous(Py_buffer *view)
{
	Py_ssize_t sd, dim;
	int i;

	if (view->ndim == 0) return 1;
	if (view->strides == NULL) return (view->ndim == 1);

	sd = view->itemsize;
	if (view->ndim == 1) return (view->shape[0] == 1 ||
				   sd == view->strides[0]);
	for (i=0; i<view->ndim; i++) {
		dim = view->shape[i];
		if (dim == 0) return 1;
		if (view->strides[i] != sd) return 0;
		sd *= dim;
	}
	return 1;
}

static int
_IsCContiguous(Py_buffer *view)
{
	Py_ssize_t sd, dim;
	int i;

	if (view->ndim == 0) return 1;
	if (view->strides == NULL) return 1;

	sd = view->itemsize;
	if (view->ndim == 1) return (view->shape[0] == 1 ||
				   sd == view->strides[0]);
	for (i=view->ndim-1; i>=0; i--) {
		dim = view->shape[i];
		if (dim == 0) return 1;
		if (view->strides[i] != sd) return 0;
		sd *= dim;
	}
	return 1;
}

int
PyBuffer_IsContiguous(Py_buffer *view, char fort)
{

	if (view->suboffsets != NULL) return 0;

	if (fort == 'C')
		return _IsCContiguous(view);
	else if (fort == 'F')
		return _IsFortranContiguous(view);
	else if (fort == 'A')
		return (_IsCContiguous(view) || _IsFortranContiguous(view));
	return 0;
}


void*
PyBuffer_GetPointer(Py_buffer *view, Py_ssize_t *indices)
{
	char* pointer;
	int i;
	pointer = (char *)view->buf;
	for (i = 0; i < view->ndim; i++) {
		pointer += view->strides[i]*indices[i];
		if ((view->suboffsets != NULL) && (view->suboffsets[i] >= 0)) {
			pointer = *((char**)pointer) + view->suboffsets[i];
		}
	}
	return (void*)pointer;
}


void
_add_one_to_index_F(int nd, Py_ssize_t *index, Py_ssize_t *shape)
{
	int k;

	for (k=0; k<nd; k++) {
		if (index[k] < shape[k]-1) {
			index[k]++;
			break;
		}
		else {
			index[k] = 0;
		}
	}
}

void
_add_one_to_index_C(int nd, Py_ssize_t *index, Py_ssize_t *shape)
{
	int k;

	for (k=nd-1; k>=0; k--) {
		if (index[k] < shape[k]-1) {
			index[k]++;
			break;
		}
		else {
			index[k] = 0;
		}
	}
}

  /* view is not checked for consistency in either of these.  It is
     assumed that the size of the buffer is view->len in
     view->len / view->itemsize elements.
  */

int
PyBuffer_ToContiguous(void *buf, Py_buffer *view, Py_ssize_t len, char fort)
{
	int k;
	void (*addone)(int, Py_ssize_t *, Py_ssize_t *);
	Py_ssize_t *indices, elements;
	char *dest, *ptr;

	if (len > view->len) {
		len = view->len;
	}

	if (PyBuffer_IsContiguous(view, fort)) {
		/* simplest copy is all that is needed */
		memcpy(buf, view->buf, len);
		return 0;
	}

	/* Otherwise a more elaborate scheme is needed */

	/* XXX(nnorwitz): need to check for overflow! */
	indices = (Py_ssize_t *)PyMem_Malloc(sizeof(Py_ssize_t)*(view->ndim));
	if (indices == NULL) {
		PyErr_NoMemory();
		return -1;
	}
	for (k=0; k<view->ndim;k++) {
		indices[k] = 0;
	}

	if (fort == 'F') {
		addone = _add_one_to_index_F;
	}
	else {
		addone = _add_one_to_index_C;
	}
	dest = buf;
	/* XXX : This is not going to be the fastest code in the world
		 several optimizations are possible.
	 */
	elements = len / view->itemsize;
	while (elements--) {
		addone(view->ndim, indices, view->shape);
		ptr = PyBuffer_GetPointer(view, indices);
		memcpy(dest, ptr, view->itemsize);
		dest += view->itemsize;
	}
	PyMem_Free(indices);
	return 0;
}

int
PyBuffer_FromContiguous(Py_buffer *view, void *buf, Py_ssize_t len, char fort)
{
	int k;
	void (*addone)(int, Py_ssize_t *, Py_ssize_t *);
	Py_ssize_t *indices, elements;
	char *src, *ptr;

	if (len > view->len) {
		len = view->len;
	}

	if (PyBuffer_IsContiguous(view, fort)) {
		/* simplest copy is all that is needed */
		memcpy(view->buf, buf, len);
		return 0;
	}

	/* Otherwise a more elaborate scheme is needed */

	/* XXX(nnorwitz): need to check for overflow! */
	indices = (Py_ssize_t *)PyMem_Malloc(sizeof(Py_ssize_t)*(view->ndim));
	if (indices == NULL) {
		PyErr_NoMemory();
		return -1;
	}
	for (k=0; k<view->ndim;k++) {
		indices[k] = 0;
	}

	if (fort == 'F') {
		addone = _add_one_to_index_F;
	}
	else {
		addone = _add_one_to_index_C;
	}
	src = buf;
	/* XXX : This is not going to be the fastest code in the world
		 several optimizations are possible.
	 */
	elements = len / view->itemsize;
	while (elements--) {
		addone(view->ndim, indices, view->shape);
		ptr = PyBuffer_GetPointer(view, indices);
		memcpy(ptr, src, view->itemsize);
		src += view->itemsize;
	}

	PyMem_Free(indices);
	return 0;
}

int PyObject_CopyData(PyObject *dest, PyObject *src)
{
	Py_buffer view_dest, view_src;
	int k;
	Py_ssize_t *indices, elements;
	char *dptr, *sptr;

	if (!PyObject_CheckBuffer(dest) ||
	    !PyObject_CheckBuffer(src)) {
		PyErr_SetString(PyExc_TypeError,
				"both destination and source must have the "\
				"buffer interface");
		return -1;
	}

	if (PyObject_GetBuffer(dest, &view_dest, PyBUF_FULL) != 0) return -1;
	if (PyObject_GetBuffer(src, &view_src, PyBUF_FULL_RO) != 0) {
		PyBuffer_Release(&view_dest);
		return -1;
	}

	if (view_dest.len < view_src.len) {
		PyErr_SetString(PyExc_BufferError,
				"destination is too small to receive data from source");
		PyBuffer_Release(&view_dest);
		PyBuffer_Release(&view_src);
		return -1;
	}

	if ((PyBuffer_IsContiguous(&view_dest, 'C') &&
	     PyBuffer_IsContiguous(&view_src, 'C')) ||
	    (PyBuffer_IsContiguous(&view_dest, 'F') &&
	     PyBuffer_IsContiguous(&view_src, 'F'))) {
		/* simplest copy is all that is needed */
		memcpy(view_dest.buf, view_src.buf, view_src.len);
		PyBuffer_Release(&view_dest);
		PyBuffer_Release(&view_src);
		return 0;
	}

	/* Otherwise a more elaborate copy scheme is needed */

	/* XXX(nnorwitz): need to check for overflow! */
	indices = (Py_ssize_t *)PyMem_Malloc(sizeof(Py_ssize_t)*view_src.ndim);
	if (indices == NULL) {
		PyErr_NoMemory();
		PyBuffer_Release(&view_dest);
		PyBuffer_Release(&view_src);
		return -1;
	}
	for (k=0; k<view_src.ndim;k++) {
		indices[k] = 0;
	}
	elements = 1;
	for (k=0; k<view_src.ndim; k++) {
		/* XXX(nnorwitz): can this overflow? */
		elements *= view_src.shape[k];
	}
	while (elements--) {
		_add_one_to_index_C(view_src.ndim, indices, view_src.shape);
		dptr = PyBuffer_GetPointer(&view_dest, indices);
		sptr = PyBuffer_GetPointer(&view_src, indices);
		memcpy(dptr, sptr, view_src.itemsize);
	}
	PyMem_Free(indices);
	PyBuffer_Release(&view_dest);
	PyBuffer_Release(&view_src);
	return 0;
}

void
PyBuffer_FillContiguousStrides(int nd, Py_ssize_t *shape,
			       Py_ssize_t *strides, int itemsize,
			       char fort)
{
	int k;
	Py_ssize_t sd;

	sd = itemsize;
	if (fort == 'F') {
		for (k=0; k<nd; k++) {
			strides[k] = sd;
			sd *= shape[k];
		}
	}
	else {
		for (k=nd-1; k>=0; k--) {
			strides[k] = sd;
			sd *= shape[k];
		}
	}
	return;
}

int
PyBuffer_FillInfo(Py_buffer *view, PyObject *obj, void *buf, Py_ssize_t len,
	      int readonly, int flags)
{
	if (view == NULL) return 0;
	if (((flags & PyBUF_WRITABLE) == PyBUF_WRITABLE) &&
	    (readonly == 1)) {
		PyErr_SetString(PyExc_BufferError,
				"Object is not writable.");
		return -1;
	}

	view->obj = obj;
	if (obj)
		Py_INCREF(obj);
	view->buf = buf;
	view->len = len;
	view->readonly = readonly;
	view->itemsize = 1;
	view->format = NULL;
	if ((flags & PyBUF_FORMAT) == PyBUF_FORMAT)
		view->format = "B";
	view->ndim = 1;
	view->shape = NULL;
	if ((flags & PyBUF_ND) == PyBUF_ND)
		view->shape = &(view->len);
	view->strides = NULL;
	if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES)
		view->strides = &(view->itemsize);
	view->suboffsets = NULL;
	view->internal = NULL;
	return 0;
}

void
PyBuffer_Release(Py_buffer *view)
{
	PyObject *obj = view->obj;
	if (obj && Py_TYPE(obj)->tp_as_buffer && Py_TYPE(obj)->tp_as_buffer->bf_releasebuffer)
		Py_TYPE(obj)->tp_as_buffer->bf_releasebuffer(obj, view);
	Py_XDECREF(obj);
	view->obj = NULL;
}

PyObject *
PyObject_Format(PyObject *obj, PyObject *format_spec)
{
    static PyObject * str__format__ = NULL;
    PyObject *meth;
    PyObject *empty = NULL;
    PyObject *result = NULL;

    /* Initialize cached value */
    if (str__format__ == NULL) {
        /* Initialize static variable needed by _PyType_Lookup */
        str__format__ = PyUnicode_FromString("__format__");
        if (str__format__ == NULL)
            goto done;
    }

    /* If no format_spec is provided, use an empty string */
    if (format_spec == NULL) {
        empty = PyUnicode_FromUnicode(NULL, 0);
        format_spec = empty;
    }

    /* Make sure the type is initialized.  float gets initialized late */
    if (Py_TYPE(obj)->tp_dict == NULL)
        if (PyType_Ready(Py_TYPE(obj)) < 0)
            goto done;

    /* Find the (unbound!) __format__ method (a borrowed reference) */
    meth = _PyType_Lookup(Py_TYPE(obj), str__format__);
    if (meth == NULL) {
        PyErr_Format(PyExc_TypeError,
                "Type %.100s doesn't define __format__",
                Py_TYPE(obj)->tp_name);
            goto done;
    }

    /* And call it, binding it to the value */
    result = PyObject_CallFunctionObjArgs(meth, obj, format_spec, NULL);

    if (result && !PyUnicode_Check(result)) {
        PyErr_SetString(PyExc_TypeError,
            "__format__ method did not return string");
        Py_DECREF(result);
        result = NULL;
        goto done;
    }

done:
    Py_XDECREF(empty);
    return result;
}
/* Operations on numbers */

int
PyNumber_Check(PyObject *o)
{
	return o && o->ob_type->tp_as_number &&
	       (o->ob_type->tp_as_number->nb_int ||
		o->ob_type->tp_as_number->nb_float);
}

/* Binary operators */

#define NB_SLOT(x) offsetof(PyNumberMethods, x)
#define NB_BINOP(nb_methods, slot) \
		(*(binaryfunc*)(& ((char*)nb_methods)[slot]))
#define NB_TERNOP(nb_methods, slot) \
		(*(ternaryfunc*)(& ((char*)nb_methods)[slot]))

/*
  Calling scheme used for binary operations:

  Order operations are tried until either a valid result or error:
	w.op(v,w)[*], v.op(v,w), w.op(v,w)

  [*] only when v->ob_type != w->ob_type && w->ob_type is a subclass of
      v->ob_type
 */

static PyObject *
binary_op1(PyObject *v, PyObject *w, const int op_slot)
{
	PyObject *x;
	binaryfunc slotv = NULL;
	binaryfunc slotw = NULL;

	if (v->ob_type->tp_as_number != NULL)
		slotv = NB_BINOP(v->ob_type->tp_as_number, op_slot);
	if (w->ob_type != v->ob_type &&
	    w->ob_type->tp_as_number != NULL) {
		slotw = NB_BINOP(w->ob_type->tp_as_number, op_slot);
		if (slotw == slotv)
			slotw = NULL;
	}
	if (slotv) {
		if (slotw && PyType_IsSubtype(w->ob_type, v->ob_type)) {
			x = slotw(v, w);
			if (x != Py_NotImplemented)
				return x;
			Py_DECREF(x); /* can't do it */
			slotw = NULL;
		}
		x = slotv(v, w);
		if (x != Py_NotImplemented)
			return x;
		Py_DECREF(x); /* can't do it */
	}
	if (slotw) {
		x = slotw(v, w);
		if (x != Py_NotImplemented)
			return x;
		Py_DECREF(x); /* can't do it */
	}
	Py_INCREF(Py_NotImplemented);
	return Py_NotImplemented;
}

static PyObject *
binop_type_error(PyObject *v, PyObject *w, const char *op_name)
{
	PyErr_Format(PyExc_TypeError,
		     "unsupported operand type(s) for %.100s: "
		     "'%.100s' and '%.100s'",
		     op_name,
		     v->ob_type->tp_name,
		     w->ob_type->tp_name);
	return NULL;
}

static PyObject *
binary_op(PyObject *v, PyObject *w, const int op_slot, const char *op_name)
{
	PyObject *result = binary_op1(v, w, op_slot);
	if (result == Py_NotImplemented) {
		Py_DECREF(result);
		return binop_type_error(v, w, op_name);
	}
	return result;
}


/*
  Calling scheme used for ternary operations:

  Order operations are tried until either a valid result or error:
	v.op(v,w,z), w.op(v,w,z), z.op(v,w,z)
 */

static PyObject *
ternary_op(PyObject *v,
	   PyObject *w,
	   PyObject *z,
	   const int op_slot,
	   const char *op_name)
{
	PyNumberMethods *mv, *mw, *mz;
	PyObject *x = NULL;
	ternaryfunc slotv = NULL;
	ternaryfunc slotw = NULL;
	ternaryfunc slotz = NULL;

	mv = v->ob_type->tp_as_number;
	mw = w->ob_type->tp_as_number;
	if (mv != NULL)
		slotv = NB_TERNOP(mv, op_slot);
	if (w->ob_type != v->ob_type &&
	    mw != NULL) {
		slotw = NB_TERNOP(mw, op_slot);
		if (slotw == slotv)
			slotw = NULL;
	}
	if (slotv) {
		if (slotw && PyType_IsSubtype(w->ob_type, v->ob_type)) {
			x = slotw(v, w, z);
			if (x != Py_NotImplemented)
				return x;
			Py_DECREF(x); /* can't do it */
			slotw = NULL;
		}
		x = slotv(v, w, z);
		if (x != Py_NotImplemented)
			return x;
		Py_DECREF(x); /* can't do it */
	}
	if (slotw) {
		x = slotw(v, w, z);
		if (x != Py_NotImplemented)
			return x;
		Py_DECREF(x); /* can't do it */
	}
	mz = z->ob_type->tp_as_number;
	if (mz != NULL) {
		slotz = NB_TERNOP(mz, op_slot);
		if (slotz == slotv || slotz == slotw)
			slotz = NULL;
		if (slotz) {
			x = slotz(v, w, z);
			if (x != Py_NotImplemented)
				return x;
			Py_DECREF(x); /* can't do it */
		}
	}

	if (z == Py_None)
		PyErr_Format(
			PyExc_TypeError,
			"unsupported operand type(s) for ** or pow(): "
			"'%.100s' and '%.100s'",
			v->ob_type->tp_name,
			w->ob_type->tp_name);
	else
		PyErr_Format(
			PyExc_TypeError,
			"unsupported operand type(s) for pow(): "
			"'%.100s', '%.100s', '%.100s'",
			v->ob_type->tp_name,
			w->ob_type->tp_name,
			z->ob_type->tp_name);
	return NULL;
}

#define BINARY_FUNC(func, op, op_name) \
    PyObject * \
    func(PyObject *v, PyObject *w) { \
	    return binary_op(v, w, NB_SLOT(op), op_name); \
    }

BINARY_FUNC(PyNumber_Or, nb_or, "|")
BINARY_FUNC(PyNumber_Xor, nb_xor, "^")
BINARY_FUNC(PyNumber_And, nb_and, "&")
BINARY_FUNC(PyNumber_Lshift, nb_lshift, "<<")
BINARY_FUNC(PyNumber_Rshift, nb_rshift, ">>")
BINARY_FUNC(PyNumber_Subtract, nb_subtract, "-")
BINARY_FUNC(PyNumber_Divmod, nb_divmod, "divmod()")

PyObject *
PyNumber_Add(PyObject *v, PyObject *w)
{
	PyObject *result = binary_op1(v, w, NB_SLOT(nb_add));
	if (result == Py_NotImplemented) {
		PySequenceMethods *m = v->ob_type->tp_as_sequence;
		Py_DECREF(result);
		if (m && m->sq_concat) {
			return (*m->sq_concat)(v, w);
		}
		result = binop_type_error(v, w, "+");
	}
	return result;
}

static PyObject *
sequence_repeat(ssizeargfunc repeatfunc, PyObject *seq, PyObject *n)
{
	Py_ssize_t count;
	if (PyIndex_Check(n)) {
		count = PyNumber_AsSsize_t(n, PyExc_OverflowError);
		if (count == -1 && PyErr_Occurred())
			return NULL;
	}
	else {
		return type_error("can't multiply sequence by "
				  "non-int of type '%.200s'", n);
	}
	return (*repeatfunc)(seq, count);
}

PyObject *
PyNumber_Multiply(PyObject *v, PyObject *w)
{
	PyObject *result = binary_op1(v, w, NB_SLOT(nb_multiply));
	if (result == Py_NotImplemented) {
		PySequenceMethods *mv = v->ob_type->tp_as_sequence;
		PySequenceMethods *mw = w->ob_type->tp_as_sequence;
		Py_DECREF(result);
		if  (mv && mv->sq_repeat) {
			return sequence_repeat(mv->sq_repeat, v, w);
		}
		else if (mw && mw->sq_repeat) {
			return sequence_repeat(mw->sq_repeat, w, v);
		}
		result = binop_type_error(v, w, "*");
	}
	return result;
}

PyObject *
PyNumber_FloorDivide(PyObject *v, PyObject *w)
{
	return binary_op(v, w, NB_SLOT(nb_floor_divide), "//");
}

PyObject *
PyNumber_TrueDivide(PyObject *v, PyObject *w)
{
	return binary_op(v, w, NB_SLOT(nb_true_divide), "/");
}

PyObject *
PyNumber_Remainder(PyObject *v, PyObject *w)
{
	return binary_op(v, w, NB_SLOT(nb_remainder), "%");
}

PyObject *
PyNumber_Power(PyObject *v, PyObject *w, PyObject *z)
{
	return ternary_op(v, w, z, NB_SLOT(nb_power), "** or pow()");
}

/* Binary in-place operators */

/* The in-place operators are defined to fall back to the 'normal',
   non in-place operations, if the in-place methods are not in place.

   - If the left hand object has the appropriate struct members, and
     they are filled, call the appropriate function and return the
     result.  No coercion is done on the arguments; the left-hand object
     is the one the operation is performed on, and it's up to the
     function to deal with the right-hand object.

   - Otherwise, in-place modification is not supported. Handle it exactly as
     a non in-place operation of the same kind.

   */

static PyObject *
binary_iop1(PyObject *v, PyObject *w, const int iop_slot, const int op_slot)
{
	PyNumberMethods *mv = v->ob_type->tp_as_number;
	if (mv != NULL) {
		binaryfunc slot = NB_BINOP(mv, iop_slot);
		if (slot) {
			PyObject *x = (slot)(v, w);
			if (x != Py_NotImplemented) {
				return x;
			}
			Py_DECREF(x);
		}
	}
	return binary_op1(v, w, op_slot);
}

static PyObject *
binary_iop(PyObject *v, PyObject *w, const int iop_slot, const int op_slot,
		const char *op_name)
{
	PyObject *result = binary_iop1(v, w, iop_slot, op_slot);
	if (result == Py_NotImplemented) {
		Py_DECREF(result);
		return binop_type_error(v, w, op_name);
	}
	return result;
}

#define INPLACE_BINOP(func, iop, op, op_name) \
	PyObject * \
	func(PyObject *v, PyObject *w) { \
		return binary_iop(v, w, NB_SLOT(iop), NB_SLOT(op), op_name); \
	}

INPLACE_BINOP(PyNumber_InPlaceOr, nb_inplace_or, nb_or, "|=")
INPLACE_BINOP(PyNumber_InPlaceXor, nb_inplace_xor, nb_xor, "^=")
INPLACE_BINOP(PyNumber_InPlaceAnd, nb_inplace_and, nb_and, "&=")
INPLACE_BINOP(PyNumber_InPlaceLshift, nb_inplace_lshift, nb_lshift, "<<=")
INPLACE_BINOP(PyNumber_InPlaceRshift, nb_inplace_rshift, nb_rshift, ">>=")
INPLACE_BINOP(PyNumber_InPlaceSubtract, nb_inplace_subtract, nb_subtract, "-=")

PyObject *
PyNumber_InPlaceFloorDivide(PyObject *v, PyObject *w)
{
	return binary_iop(v, w, NB_SLOT(nb_inplace_floor_divide),
			  NB_SLOT(nb_floor_divide), "//=");
}

PyObject *
PyNumber_InPlaceTrueDivide(PyObject *v, PyObject *w)
{
	return binary_iop(v, w, NB_SLOT(nb_inplace_true_divide),
			  NB_SLOT(nb_true_divide), "/=");
}

PyObject *
PyNumber_InPlaceAdd(PyObject *v, PyObject *w)
{
	PyObject *result = binary_iop1(v, w, NB_SLOT(nb_inplace_add),
				       NB_SLOT(nb_add));
	if (result == Py_NotImplemented) {
		PySequenceMethods *m = v->ob_type->tp_as_sequence;
		Py_DECREF(result);
		if (m != NULL) {
			binaryfunc f = NULL;
			f = m->sq_inplace_concat;
			if (f == NULL)
				f = m->sq_concat;
			if (f != NULL)
				return (*f)(v, w);
		}
		result = binop_type_error(v, w, "+=");
	}
	return result;
}

PyObject *
PyNumber_InPlaceMultiply(PyObject *v, PyObject *w)
{
	PyObject *result = binary_iop1(v, w, NB_SLOT(nb_inplace_multiply),
				       NB_SLOT(nb_multiply));
	if (result == Py_NotImplemented) {
		ssizeargfunc f = NULL;
		PySequenceMethods *mv = v->ob_type->tp_as_sequence;
		PySequenceMethods *mw = w->ob_type->tp_as_sequence;
		Py_DECREF(result);
		if (mv != NULL) {
			f = mv->sq_inplace_repeat;
			if (f == NULL)
				f = mv->sq_repeat;
			if (f != NULL)
				return sequence_repeat(f, v, w);
		}
		else if (mw != NULL) {
			/* Note that the right hand operand should not be
			 * mutated in this case so sq_inplace_repeat is not
			 * used. */
			if (mw->sq_repeat)
				return sequence_repeat(mw->sq_repeat, w, v);
		}
		result = binop_type_error(v, w, "*=");
	}
	return result;
}

PyObject *
PyNumber_InPlaceRemainder(PyObject *v, PyObject *w)
{
	return binary_iop(v, w, NB_SLOT(nb_inplace_remainder),
				NB_SLOT(nb_remainder), "%=");
}

PyObject *
PyNumber_InPlacePower(PyObject *v, PyObject *w, PyObject *z)
{
	if (v->ob_type->tp_as_number &&
	    v->ob_type->tp_as_number->nb_inplace_power != NULL) {
		return ternary_op(v, w, z, NB_SLOT(nb_inplace_power), "**=");
	}
	else {
		return ternary_op(v, w, z, NB_SLOT(nb_power), "**=");
	}
}


/* Unary operators and functions */

PyObject *
PyNumber_Negative(PyObject *o)
{
	PyNumberMethods *m;

	if (o == NULL)
		return null_error();
	m = o->ob_type->tp_as_number;
	if (m && m->nb_negative)
		return (*m->nb_negative)(o);

	return type_error("bad operand type for unary -: '%.200s'", o);
}

PyObject *
PyNumber_Positive(PyObject *o)
{
	PyNumberMethods *m;

	if (o == NULL)
		return null_error();
	m = o->ob_type->tp_as_number;
	if (m && m->nb_positive)
		return (*m->nb_positive)(o);

	return type_error("bad operand type for unary +: '%.200s'", o);
}

PyObject *
PyNumber_Invert(PyObject *o)
{
	PyNumberMethods *m;

	if (o == NULL)
		return null_error();
	m = o->ob_type->tp_as_number;
	if (m && m->nb_invert)
		return (*m->nb_invert)(o);

	return type_error("bad operand type for unary ~: '%.200s'", o);
}

PyObject *
PyNumber_Absolute(PyObject *o)
{
	PyNumberMethods *m;

	if (o == NULL)
		return null_error();
	m = o->ob_type->tp_as_number;
	if (m && m->nb_absolute)
		return m->nb_absolute(o);

	return type_error("bad operand type for abs(): '%.200s'", o);
}

/* Return a Python Int or Long from the object item
   Raise TypeError if the result is not an int-or-long
   or if the object cannot be interpreted as an index.
*/
PyObject *
PyNumber_Index(PyObject *item)
{
	PyObject *result = NULL;
	if (item == NULL)
		return null_error();
	if (PyLong_Check(item)) {
		Py_INCREF(item);
		return item;
	}
	if (PyIndex_Check(item)) {
		result = item->ob_type->tp_as_number->nb_index(item);
		if (result && !PyLong_Check(result)) {
			PyErr_Format(PyExc_TypeError,
				     "__index__ returned non-int "
				     "(type %.200s)",
				     result->ob_type->tp_name);
			Py_DECREF(result);
			return NULL;
		}
	}
	else {
		PyErr_Format(PyExc_TypeError,
			     "'%.200s' object cannot be interpreted "
			     "as an integer", item->ob_type->tp_name);
	}
	return result;
}

/* Return an error on Overflow only if err is not NULL*/

Py_ssize_t
PyNumber_AsSsize_t(PyObject *item, PyObject *err)
{
	Py_ssize_t result;
	PyObject *runerr;
	PyObject *value = PyNumber_Index(item);
	if (value == NULL)
		return -1;

	/* We're done if PyLong_AsSsize_t() returns without error. */
	result = PyLong_AsSsize_t(value);
	if (result != -1 || !(runerr = PyErr_Occurred()))
		goto finish;

	/* Error handling code -- only manage OverflowError differently */
	if (!PyErr_GivenExceptionMatches(runerr, PyExc_OverflowError))
		goto finish;

	PyErr_Clear();
	/* If no error-handling desired then the default clipping
	   is sufficient.
	 */
	if (!err) {
		assert(PyLong_Check(value));
		/* Whether or not it is less than or equal to
		   zero is determined by the sign of ob_size
		*/
		if (_PyLong_Sign(value) < 0)
			result = PY_SSIZE_T_MIN;
		else
			result = PY_SSIZE_T_MAX;
	}
	else {
		/* Otherwise replace the error with caller's error object. */
		PyErr_Format(err,
			     "cannot fit '%.200s' into an index-sized integer",
			     item->ob_type->tp_name);
	}

 finish:
	Py_DECREF(value);
	return result;
}


PyObject *
_PyNumber_ConvertIntegralToInt(PyObject *integral, const char* error_format)
{
	static PyObject *int_name = NULL;
	if (int_name == NULL) {
		int_name = PyUnicode_InternFromString("__int__");
		if (int_name == NULL)
			return NULL;
	}

	if (integral && !PyLong_Check(integral)) { 
		/* Don't go through tp_as_number->nb_int to avoid
		   hitting the classic class fallback to __trunc__. */
		PyObject *int_func = PyObject_GetAttr(integral, int_name);
		if (int_func == NULL) {
			PyErr_Clear(); /* Raise a different error. */
			goto non_integral_error;
		}
		Py_DECREF(integral);
		integral = PyEval_CallObject(int_func, NULL);
		Py_DECREF(int_func);
		if (integral && !PyLong_Check(integral)) { 
			goto non_integral_error;
		}
	}
	return integral;

non_integral_error:
	PyErr_Format(PyExc_TypeError, error_format, Py_TYPE(integral)->tp_name);
	Py_DECREF(integral);
	return NULL;
}


/* Add a check for embedded NULL-bytes in the argument. */
static PyObject *
long_from_string(const char *s, Py_ssize_t len)
{
	char *end;
	PyObject *x;

	x = PyLong_FromString((char*)s, &end, 10);
	if (x == NULL)
		return NULL;
	if (end != s + len) {
		PyErr_SetString(PyExc_ValueError,
				"null byte in argument for int()");
		Py_DECREF(x);
		return NULL;
	}
	return x;
}

PyObject *
PyNumber_Long(PyObject *o)
{
	PyNumberMethods *m;
	static PyObject *trunc_name = NULL;
	PyObject *trunc_func;
	const char *buffer;
	Py_ssize_t buffer_len;

	if (trunc_name == NULL) {
		trunc_name = PyUnicode_InternFromString("__trunc__");
		if (trunc_name == NULL)
			return NULL;
	}

	if (o == NULL)
		return null_error();
	if (PyLong_CheckExact(o)) {
		Py_INCREF(o);
		return o;
	}
	m = o->ob_type->tp_as_number;
	if (m && m->nb_int) { /* This should include subclasses of int */
		PyObject *res = m->nb_int(o);
		if (res && !PyLong_Check(res)) {
			PyErr_Format(PyExc_TypeError,
				     "__int__ returned non-int (type %.200s)",
				     res->ob_type->tp_name);
			Py_DECREF(res);
			return NULL;
		}
		return res;
	}
	if (PyLong_Check(o)) /* An int subclass without nb_int */
		return _PyLong_Copy((PyLongObject *)o);
	trunc_func = PyObject_GetAttr(o, trunc_name);
	if (trunc_func) {
		PyObject *truncated = PyEval_CallObject(trunc_func, NULL);
		PyObject *int_instance;
		Py_DECREF(trunc_func);
		/* __trunc__ is specified to return an Integral type,
		   but long() needs to return a long. */
		int_instance = _PyNumber_ConvertIntegralToInt(
			truncated,
			"__trunc__ returned non-Integral (type %.200s)");
		return int_instance;
	}
	PyErr_Clear();  /* It's not an error if  o.__trunc__ doesn't exist. */

	if (PyBytes_Check(o))
		/* need to do extra error checking that PyLong_FromString()
		 * doesn't do.  In particular long('9.5') must raise an
		 * exception, not truncate the float.
		 */
		return long_from_string(PyBytes_AS_STRING(o),
					PyBytes_GET_SIZE(o));
	if (PyUnicode_Check(o))
		/* The above check is done in PyLong_FromUnicode(). */
		return PyLong_FromUnicode(PyUnicode_AS_UNICODE(o),
					  PyUnicode_GET_SIZE(o),
					  10);
	if (!PyObject_AsCharBuffer(o, &buffer, &buffer_len))
		return long_from_string(buffer, buffer_len);

	return type_error("int() argument must be a string or a "
			  "number, not '%.200s'", o);
}

PyObject *
PyNumber_Float(PyObject *o)
{
	PyNumberMethods *m;

	if (o == NULL)
		return null_error();
	m = o->ob_type->tp_as_number;
	if (m && m->nb_float) { /* This should include subclasses of float */
		PyObject *res = m->nb_float(o);
		if (res && !PyFloat_Check(res)) {
			PyErr_Format(PyExc_TypeError,
			  "__float__ returned non-float (type %.200s)",
			  res->ob_type->tp_name);
			Py_DECREF(res);
			return NULL;
		}
		return res;
	}
	if (PyFloat_Check(o)) { /* A float subclass with nb_float == NULL */
		PyFloatObject *po = (PyFloatObject *)o;
		return PyFloat_FromDouble(po->ob_fval);
	}
	return PyFloat_FromString(o);
}


PyObject *
PyNumber_ToBase(PyObject *n, int base)
{
	PyObject *res = NULL;
	PyObject *index = PyNumber_Index(n);

	if (!index)
		return NULL;
	if (PyLong_Check(index))
		res = _PyLong_Format(index, base);
	else
		/* It should not be possible to get here, as
		   PyNumber_Index already has a check for the same
		   condition */
		PyErr_SetString(PyExc_ValueError, "PyNumber_ToBase: index not "
				"int or long");
	Py_DECREF(index);
	return res;
}


/* Operations on sequences */

int
PySequence_Check(PyObject *s)
{
	if (PyDict_Check(s))
		return 0;
	return s != NULL && s->ob_type->tp_as_sequence &&
		s->ob_type->tp_as_sequence->sq_item != NULL;
}

Py_ssize_t
PySequence_Size(PyObject *s)
{
	PySequenceMethods *m;

	if (s == NULL) {
		null_error();
		return -1;
	}

	m = s->ob_type->tp_as_sequence;
	if (m && m->sq_length)
		return m->sq_length(s);

	type_error("object of type '%.200s' has no len()", s);
	return -1;
}

#undef PySequence_Length
Py_ssize_t
PySequence_Length(PyObject *s)
{
	return PySequence_Size(s);
}
#define PySequence_Length PySequence_Size

PyObject *
PySequence_Concat(PyObject *s, PyObject *o)
{
	PySequenceMethods *m;

	if (s == NULL || o == NULL)
		return null_error();

	m = s->ob_type->tp_as_sequence;
	if (m && m->sq_concat)
		return m->sq_concat(s, o);

	/* Instances of user classes defining an __add__() method only
	   have an nb_add slot, not an sq_concat slot.	So we fall back
	   to nb_add if both arguments appear to be sequences. */
	if (PySequence_Check(s) && PySequence_Check(o)) {
		PyObject *result = binary_op1(s, o, NB_SLOT(nb_add));
		if (result != Py_NotImplemented)
			return result;
		Py_DECREF(result);
	}
	return type_error("'%.200s' object can't be concatenated", s);
}

PyObject *
PySequence_Repeat(PyObject *o, Py_ssize_t count)
{
	PySequenceMethods *m;

	if (o == NULL)
		return null_error();

	m = o->ob_type->tp_as_sequence;
	if (m && m->sq_repeat)
		return m->sq_repeat(o, count);

	/* Instances of user classes defining a __mul__() method only
	   have an nb_multiply slot, not an sq_repeat slot. so we fall back
	   to nb_multiply if o appears to be a sequence. */
	if (PySequence_Check(o)) {
		PyObject *n, *result;
		n = PyLong_FromSsize_t(count);
		if (n == NULL)
			return NULL;
		result = binary_op1(o, n, NB_SLOT(nb_multiply));
		Py_DECREF(n);
		if (result != Py_NotImplemented)
			return result;
		Py_DECREF(result);
	}
	return type_error("'%.200s' object can't be repeated", o);
}

PyObject *
PySequence_InPlaceConcat(PyObject *s, PyObject *o)
{
	PySequenceMethods *m;

	if (s == NULL || o == NULL)
		return null_error();

	m = s->ob_type->tp_as_sequence;
	if (m && m->sq_inplace_concat)
		return m->sq_inplace_concat(s, o);
	if (m && m->sq_concat)
		return m->sq_concat(s, o);

	if (PySequence_Check(s) && PySequence_Check(o)) {
		PyObject *result = binary_iop1(s, o, NB_SLOT(nb_inplace_add),
					       NB_SLOT(nb_add));
		if (result != Py_NotImplemented)
			return result;
		Py_DECREF(result);
	}
	return type_error("'%.200s' object can't be concatenated", s);
}

PyObject *
PySequence_InPlaceRepeat(PyObject *o, Py_ssize_t count)
{
	PySequenceMethods *m;

	if (o == NULL)
		return null_error();

	m = o->ob_type->tp_as_sequence;
	if (m && m->sq_inplace_repeat)
		return m->sq_inplace_repeat(o, count);
	if (m && m->sq_repeat)
		return m->sq_repeat(o, count);

	if (PySequence_Check(o)) {
		PyObject *n, *result;
		n = PyLong_FromSsize_t(count);
		if (n == NULL)
			return NULL;
		result = binary_iop1(o, n, NB_SLOT(nb_inplace_multiply),
				     NB_SLOT(nb_multiply));
		Py_DECREF(n);
		if (result != Py_NotImplemented)
			return result;
		Py_DECREF(result);
	}
	return type_error("'%.200s' object can't be repeated", o);
}

PyObject *
PySequence_GetItem(PyObject *s, Py_ssize_t i)
{
	PySequenceMethods *m;

	if (s == NULL)
		return null_error();

	m = s->ob_type->tp_as_sequence;
	if (m && m->sq_item) {
		if (i < 0) {
			if (m->sq_length) {
				Py_ssize_t l = (*m->sq_length)(s);
				if (l < 0)
					return NULL;
				i += l;
			}
		}
		return m->sq_item(s, i);
	}

	return type_error("'%.200s' object does not support indexing", s);
}

PyObject *
PySequence_GetSlice(PyObject *s, Py_ssize_t i1, Py_ssize_t i2)
{
	PyMappingMethods *mp;

	if (!s) return null_error();

	mp = s->ob_type->tp_as_mapping;
	if (mp->mp_subscript) {
		PyObject *res;
		PyObject *slice = _PySlice_FromIndices(i1, i2);
		if (!slice)
			return NULL;
		res = mp->mp_subscript(s, slice);
		Py_DECREF(slice);
		return res;
	}

	return type_error("'%.200s' object is unsliceable", s);
}

int
PySequence_SetItem(PyObject *s, Py_ssize_t i, PyObject *o)
{
	PySequenceMethods *m;

	if (s == NULL) {
		null_error();
		return -1;
	}

	m = s->ob_type->tp_as_sequence;
	if (m && m->sq_ass_item) {
		if (i < 0) {
			if (m->sq_length) {
				Py_ssize_t l = (*m->sq_length)(s);
				if (l < 0)
					return -1;
				i += l;
			}
		}
		return m->sq_ass_item(s, i, o);
	}

	type_error("'%.200s' object does not support item assignment", s);
	return -1;
}

int
PySequence_DelItem(PyObject *s, Py_ssize_t i)
{
	PySequenceMethods *m;

	if (s == NULL) {
		null_error();
		return -1;
	}

	m = s->ob_type->tp_as_sequence;
	if (m && m->sq_ass_item) {
		if (i < 0) {
			if (m->sq_length) {
				Py_ssize_t l = (*m->sq_length)(s);
				if (l < 0)
					return -1;
				i += l;
			}
		}
		return m->sq_ass_item(s, i, (PyObject *)NULL);
	}

	type_error("'%.200s' object doesn't support item deletion", s);
	return -1;
}

int
PySequence_SetSlice(PyObject *s, Py_ssize_t i1, Py_ssize_t i2, PyObject *o)
{
	PyMappingMethods *mp;

	if (s == NULL) {
		null_error();
		return -1;
	}

	mp = s->ob_type->tp_as_mapping;
	if (mp->mp_ass_subscript) {
		int res;
		PyObject *slice = _PySlice_FromIndices(i1, i2);
		if (!slice)
			return -1;
		res = mp->mp_ass_subscript(s, slice, o);
		Py_DECREF(slice);
		return res;
	}

	type_error("'%.200s' object doesn't support slice assignment", s);
	return -1;
}

int
PySequence_DelSlice(PyObject *s, Py_ssize_t i1, Py_ssize_t i2)
{
	PyMappingMethods *mp;

	if (s == NULL) {
		null_error();
		return -1;
	}

	mp = s->ob_type->tp_as_mapping;
	if (mp->mp_ass_subscript) {
		int res;
		PyObject *slice = _PySlice_FromIndices(i1, i2);
		if (!slice)
			return -1;
		res = mp->mp_ass_subscript(s, slice, NULL);
		Py_DECREF(slice);
		return res;
	}
	type_error("'%.200s' object doesn't support slice deletion", s);
	return -1;
}

PyObject *
PySequence_Tuple(PyObject *v)
{
	PyObject *it;  /* iter(v) */
	Py_ssize_t n;	      /* guess for result tuple size */
	PyObject *result = NULL;
	Py_ssize_t j;

	if (v == NULL)
		return null_error();

	/* Special-case the common tuple and list cases, for efficiency. */
	if (PyTuple_CheckExact(v)) {
		/* Note that we can't know whether it's safe to return
		   a tuple *subclass* instance as-is, hence the restriction
		   to exact tuples here.  In contrast, lists always make
		   a copy, so there's no need for exactness below. */
		Py_INCREF(v);
		return v;
	}
	if (PyList_Check(v))
		return PyList_AsTuple(v);

	/* Get iterator. */
	it = PyObject_GetIter(v);
	if (it == NULL)
		return NULL;

	/* Guess result size and allocate space. */
	n = _PyObject_LengthHint(v, 10);
	if (n == -1)
		goto Fail;
	result = PyTuple_New(n);
	if (result == NULL)
		goto Fail;

	/* Fill the tuple. */
	for (j = 0; ; ++j) {
		PyObject *item = PyIter_Next(it);
		if (item == NULL) {
			if (PyErr_Occurred())
				goto Fail;
			break;
		}
		if (j >= n) {
			Py_ssize_t oldn = n;
			/* The over-allocation strategy can grow a bit faster
			   than for lists because unlike lists the
			   over-allocation isn't permanent -- we reclaim
			   the excess before the end of this routine.
			   So, grow by ten and then add 25%.
			*/
			n += 10;
			n += n >> 2;
			if (n < oldn) {
				/* Check for overflow */
				PyErr_NoMemory();
				Py_DECREF(item);
				goto Fail;
			}
			if (_PyTuple_Resize(&result, n) != 0) {
				Py_DECREF(item);
				goto Fail;
			}
		}
		PyTuple_SET_ITEM(result, j, item);
	}

	/* Cut tuple back if guess was too large. */
	if (j < n &&
	    _PyTuple_Resize(&result, j) != 0)
		goto Fail;

	Py_DECREF(it);
	return result;

Fail:
	Py_XDECREF(result);
	Py_DECREF(it);
	return NULL;
}

PyObject *
PySequence_List(PyObject *v)
{
	PyObject *result;  /* result list */
	PyObject *rv;	   /* return value from PyList_Extend */

	if (v == NULL)
		return null_error();

	result = PyList_New(0);
	if (result == NULL)
		return NULL;

	rv = _PyList_Extend((PyListObject *)result, v);
	if (rv == NULL) {
		Py_DECREF(result);
		return NULL;
	}
	Py_DECREF(rv);
	return result;
}

PyObject *
PySequence_Fast(PyObject *v, const char *m)
{
	PyObject *it;

	if (v == NULL)
		return null_error();

	if (PyList_CheckExact(v) || PyTuple_CheckExact(v)) {
		Py_INCREF(v);
		return v;
	}

	it = PyObject_GetIter(v);
	if (it == NULL) {
		if (PyErr_ExceptionMatches(PyExc_TypeError))
			PyErr_SetString(PyExc_TypeError, m);
		return NULL;
	}

	v = PySequence_List(it);
	Py_DECREF(it);

	return v;
}

/* Iterate over seq.  Result depends on the operation:
   PY_ITERSEARCH_COUNT:	 -1 if error, else # of times obj appears in seq.
   PY_ITERSEARCH_INDEX:	 0-based index of first occurrence of obj in seq;
	set ValueError and return -1 if none found; also return -1 on error.
   Py_ITERSEARCH_CONTAINS:  return 1 if obj in seq, else 0; -1 on error.
*/
Py_ssize_t
_PySequence_IterSearch(PyObject *seq, PyObject *obj, int operation)
{
	Py_ssize_t n;
	int wrapped;  /* for PY_ITERSEARCH_INDEX, true iff n wrapped around */
	PyObject *it;  /* iter(seq) */

	if (seq == NULL || obj == NULL) {
		null_error();
		return -1;
	}

	it = PyObject_GetIter(seq);
	if (it == NULL) {
		type_error("argument of type '%.200s' is not iterable", seq);
		return -1;
	}

	n = wrapped = 0;
	for (;;) {
		int cmp;
		PyObject *item = PyIter_Next(it);
		if (item == NULL) {
			if (PyErr_Occurred())
				goto Fail;
			break;
		}

		cmp = PyObject_RichCompareBool(obj, item, Py_EQ);
		Py_DECREF(item);
		if (cmp < 0)
			goto Fail;
		if (cmp > 0) {
			switch (operation) {
			case PY_ITERSEARCH_COUNT:
				if (n == PY_SSIZE_T_MAX) {
					PyErr_SetString(PyExc_OverflowError,
					       "count exceeds C integer size");
					goto Fail;
				}
				++n;
				break;

			case PY_ITERSEARCH_INDEX:
				if (wrapped) {
					PyErr_SetString(PyExc_OverflowError,
					       "index exceeds C integer size");
					goto Fail;
				}
				goto Done;

			case PY_ITERSEARCH_CONTAINS:
				n = 1;
				goto Done;

			default:
				assert(!"unknown operation");
			}
		}

		if (operation == PY_ITERSEARCH_INDEX) {
			if (n == PY_SSIZE_T_MAX)
				wrapped = 1;
			++n;
		}
	}

	if (operation != PY_ITERSEARCH_INDEX)
		goto Done;

	PyErr_SetString(PyExc_ValueError,
			"sequence.index(x): x not in sequence");
	/* fall into failure code */
Fail:
	n = -1;
	/* fall through */
Done:
	Py_DECREF(it);
	return n;

}

/* Return # of times o appears in s. */
Py_ssize_t
PySequence_Count(PyObject *s, PyObject *o)
{
	return _PySequence_IterSearch(s, o, PY_ITERSEARCH_COUNT);
}

/* Return -1 if error; 1 if ob in seq; 0 if ob not in seq.
 * Use sq_contains if possible, else defer to _PySequence_IterSearch().
 */
int
PySequence_Contains(PyObject *seq, PyObject *ob)
{
	Py_ssize_t result;
	PySequenceMethods *sqm = seq->ob_type->tp_as_sequence;
	if (sqm != NULL && sqm->sq_contains != NULL)
		return (*sqm->sq_contains)(seq, ob);
	result = _PySequence_IterSearch(seq, ob, PY_ITERSEARCH_CONTAINS);
	return Py_SAFE_DOWNCAST(result, Py_ssize_t, int);
}

/* Backwards compatibility */
#undef PySequence_In
int
PySequence_In(PyObject *w, PyObject *v)
{
	return PySequence_Contains(w, v);
}

Py_ssize_t
PySequence_Index(PyObject *s, PyObject *o)
{
	return _PySequence_IterSearch(s, o, PY_ITERSEARCH_INDEX);
}

/* Operations on mappings */

int
PyMapping_Check(PyObject *o)
{
	return	o && o->ob_type->tp_as_mapping &&
		o->ob_type->tp_as_mapping->mp_subscript;
}

Py_ssize_t
PyMapping_Size(PyObject *o)
{
	PyMappingMethods *m;

	if (o == NULL) {
		null_error();
		return -1;
	}

	m = o->ob_type->tp_as_mapping;
	if (m && m->mp_length)
		return m->mp_length(o);

	type_error("object of type '%.200s' has no len()", o);
	return -1;
}

#undef PyMapping_Length
Py_ssize_t
PyMapping_Length(PyObject *o)
{
	return PyMapping_Size(o);
}
#define PyMapping_Length PyMapping_Size

PyObject *
PyMapping_GetItemString(PyObject *o, char *key)
{
	PyObject *okey, *r;

	if (key == NULL)
		return null_error();

	okey = PyUnicode_FromString(key);
	if (okey == NULL)
		return NULL;
	r = PyObject_GetItem(o, okey);
	Py_DECREF(okey);
	return r;
}

int
PyMapping_SetItemString(PyObject *o, char *key, PyObject *value)
{
	PyObject *okey;
	int r;

	if (key == NULL) {
		null_error();
		return -1;
	}

	okey = PyUnicode_FromString(key);
	if (okey == NULL)
		return -1;
	r = PyObject_SetItem(o, okey, value);
	Py_DECREF(okey);
	return r;
}

int
PyMapping_HasKeyString(PyObject *o, char *key)
{
	PyObject *v;

	v = PyMapping_GetItemString(o, key);
	if (v) {
		Py_DECREF(v);
		return 1;
	}
	PyErr_Clear();
	return 0;
}

int
PyMapping_HasKey(PyObject *o, PyObject *key)
{
	PyObject *v;

	v = PyObject_GetItem(o, key);
	if (v) {
		Py_DECREF(v);
		return 1;
	}
	PyErr_Clear();
	return 0;
}

PyObject *
PyMapping_Keys(PyObject *o)
{
	PyObject *keys;
	PyObject *fast;

	if (PyDict_CheckExact(o))
		return PyDict_Keys(o);
	keys = PyObject_CallMethod(o, "keys", NULL);
	if (keys == NULL)
		return NULL;
	fast = PySequence_Fast(keys, "o.keys() are not iterable");
	Py_DECREF(keys);
	return fast;
}

PyObject *
PyMapping_Items(PyObject *o)
{
	PyObject *items;
	PyObject *fast;

	if (PyDict_CheckExact(o))
		return PyDict_Items(o);
	items = PyObject_CallMethod(o, "items", NULL);
	if (items == NULL)
		return NULL;
	fast = PySequence_Fast(items, "o.items() are not iterable");
	Py_DECREF(items);
	return fast;
}

PyObject *
PyMapping_Values(PyObject *o)
{
	PyObject *values;
	PyObject *fast;

	if (PyDict_CheckExact(o))
		return PyDict_Values(o);
	values = PyObject_CallMethod(o, "values", NULL);
	if (values == NULL)
		return NULL;
	fast = PySequence_Fast(values, "o.values() are not iterable");
	Py_DECREF(values);
	return fast;
}

/* Operations on callable objects */

/* XXX PyCallable_Check() is in object.c */

PyObject *
PyObject_CallObject(PyObject *o, PyObject *a)
{
	return PyEval_CallObjectWithKeywords(o, a, NULL);
}

PyObject *
PyObject_Call(PyObject *func, PyObject *arg, PyObject *kw)
{
	ternaryfunc call;

	if ((call = func->ob_type->tp_call) != NULL) {
		PyObject *result;
		if (Py_EnterRecursiveCall(" while calling a Python object"))
		    return NULL;
		result = (*call)(func, arg, kw);
		Py_LeaveRecursiveCall();
		if (result == NULL && !PyErr_Occurred())
			PyErr_SetString(
				PyExc_SystemError,
				"NULL result without error in PyObject_Call");
		return result;
	}
	PyErr_Format(PyExc_TypeError, "'%.200s' object is not callable",
		     func->ob_type->tp_name);
	return NULL;
}

static PyObject*
call_function_tail(PyObject *callable, PyObject *args)
{
	PyObject *retval;

	if (args == NULL)
		return NULL;

	if (!PyTuple_Check(args)) {
		PyObject *a;

		a = PyTuple_New(1);
		if (a == NULL) {
			Py_DECREF(args);
			return NULL;
		}
		PyTuple_SET_ITEM(a, 0, args);
		args = a;
	}
	retval = PyObject_Call(callable, args, NULL);

	Py_DECREF(args);

	return retval;
}

PyObject *
PyObject_CallFunction(PyObject *callable, char *format, ...)
{
	va_list va;
	PyObject *args;

	if (callable == NULL)
		return null_error();

	if (format && *format) {
		va_start(va, format);
		args = Py_VaBuildValue(format, va);
		va_end(va);
	}
	else
		args = PyTuple_New(0);

	return call_function_tail(callable, args);
}

PyObject *
_PyObject_CallFunction_SizeT(PyObject *callable, char *format, ...)
{
	va_list va;
	PyObject *args;

	if (callable == NULL)
		return null_error();

	if (format && *format) {
		va_start(va, format);
		args = _Py_VaBuildValue_SizeT(format, va);
		va_end(va);
	}
	else
		args = PyTuple_New(0);

	return call_function_tail(callable, args);
}

PyObject *
PyObject_CallMethod(PyObject *o, char *name, char *format, ...)
{
	va_list va;
	PyObject *args;
	PyObject *func = NULL;
	PyObject *retval = NULL;

	if (o == NULL || name == NULL)
		return null_error();

	func = PyObject_GetAttrString(o, name);
	if (func == NULL) {
		PyErr_SetString(PyExc_AttributeError, name);
		return 0;
	}

	if (!PyCallable_Check(func)) {
		type_error("attribute of type '%.200s' is not callable", func);
		goto exit;
	}

	if (format && *format) {
		va_start(va, format);
		args = Py_VaBuildValue(format, va);
		va_end(va);
	}
	else
		args = PyTuple_New(0);

	retval = call_function_tail(func, args);

  exit:
	/* args gets consumed in call_function_tail */
	Py_XDECREF(func);

	return retval;
}

PyObject *
_PyObject_CallMethod_SizeT(PyObject *o, char *name, char *format, ...)
{
	va_list va;
	PyObject *args;
	PyObject *func = NULL;
	PyObject *retval = NULL;

	if (o == NULL || name == NULL)
		return null_error();

	func = PyObject_GetAttrString(o, name);
	if (func == NULL) {
		PyErr_SetString(PyExc_AttributeError, name);
		return 0;
	}

	if (!PyCallable_Check(func)) {
		type_error("attribute of type '%.200s' is not callable", func);
		goto exit;
	}

	if (format && *format) {
		va_start(va, format);
		args = _Py_VaBuildValue_SizeT(format, va);
		va_end(va);
	}
	else
		args = PyTuple_New(0);

	retval = call_function_tail(func, args);

  exit:
	/* args gets consumed in call_function_tail */
	Py_XDECREF(func);

	return retval;
}


static PyObject *
objargs_mktuple(va_list va)
{
	int i, n = 0;
	va_list countva;
	PyObject *result, *tmp;

#ifdef VA_LIST_IS_ARRAY
	memcpy(countva, va, sizeof(va_list));
#else
#ifdef __va_copy
	__va_copy(countva, va);
#else
	countva = va;
#endif
#endif

	while (((PyObject *)va_arg(countva, PyObject *)) != NULL)
		++n;
	result = PyTuple_New(n);
	if (result != NULL && n > 0) {
		for (i = 0; i < n; ++i) {
			tmp = (PyObject *)va_arg(va, PyObject *);
			PyTuple_SET_ITEM(result, i, tmp);
			Py_INCREF(tmp);
		}
	}
	return result;
}

PyObject *
PyObject_CallMethodObjArgs(PyObject *callable, PyObject *name, ...)
{
	PyObject *args, *tmp;
	va_list vargs;

	if (callable == NULL || name == NULL)
		return null_error();

	callable = PyObject_GetAttr(callable, name);
	if (callable == NULL)
		return NULL;

	/* count the args */
	va_start(vargs, name);
	args = objargs_mktuple(vargs);
	va_end(vargs);
	if (args == NULL) {
		Py_DECREF(callable);
		return NULL;
	}
	tmp = PyObject_Call(callable, args, NULL);
	Py_DECREF(args);
	Py_DECREF(callable);

	return tmp;
}

PyObject *
PyObject_CallFunctionObjArgs(PyObject *callable, ...)
{
	PyObject *args, *tmp;
	va_list vargs;

	if (callable == NULL)
		return null_error();

	/* count the args */
	va_start(vargs, callable);
	args = objargs_mktuple(vargs);
	va_end(vargs);
	if (args == NULL)
		return NULL;
	tmp = PyObject_Call(callable, args, NULL);
	Py_DECREF(args);

	return tmp;
}


/* isinstance(), issubclass() */

/* abstract_get_bases() has logically 4 return states, with a sort of 0th
 * state that will almost never happen.
 *
 * 0. creating the __bases__ static string could get a MemoryError
 * 1. getattr(cls, '__bases__') could raise an AttributeError
 * 2. getattr(cls, '__bases__') could raise some other exception
 * 3. getattr(cls, '__bases__') could return a tuple
 * 4. getattr(cls, '__bases__') could return something other than a tuple
 *
 * Only state #3 is a non-error state and only it returns a non-NULL object
 * (it returns the retrieved tuple).
 *
 * Any raised AttributeErrors are masked by clearing the exception and
 * returning NULL.  If an object other than a tuple comes out of __bases__,
 * then again, the return value is NULL.  So yes, these two situations
 * produce exactly the same results: NULL is returned and no error is set.
 *
 * If some exception other than AttributeError is raised, then NULL is also
 * returned, but the exception is not cleared.	That's because we want the
 * exception to be propagated along.
 *
 * Callers are expected to test for PyErr_Occurred() when the return value
 * is NULL to decide whether a valid exception should be propagated or not.
 * When there's no exception to propagate, it's customary for the caller to
 * set a TypeError.
 */
static PyObject *
abstract_get_bases(PyObject *cls)
{
	static PyObject *__bases__ = NULL;
	PyObject *bases;

	if (__bases__ == NULL) {
		__bases__ = PyUnicode_InternFromString("__bases__");
		if (__bases__ == NULL)
			return NULL;
	}
	Py_ALLOW_RECURSION
	bases = PyObject_GetAttr(cls, __bases__);
	Py_END_ALLOW_RECURSION
	if (bases == NULL) {
		if (PyErr_ExceptionMatches(PyExc_AttributeError))
			PyErr_Clear();
		return NULL;
	}
	if (!PyTuple_Check(bases)) {
		Py_DECREF(bases);
		return NULL;
	}
	return bases;
}


static int
abstract_issubclass(PyObject *derived, PyObject *cls)
{
	PyObject *bases = NULL;
	Py_ssize_t i, n;
	int r = 0;

	while (1) {
		if (derived == cls)
			return 1;
		bases = abstract_get_bases(derived);
		if (bases == NULL) {
			if (PyErr_Occurred())
				return -1;
			return 0;
		}
		n = PyTuple_GET_SIZE(bases);
		if (n == 0) {
			Py_DECREF(bases);
			return 0;
		}
		/* Avoid recursivity in the single inheritance case */
		if (n == 1) {
			derived = PyTuple_GET_ITEM(bases, 0);
			Py_DECREF(bases);
			continue;
		}
		for (i = 0; i < n; i++) {
			r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
			if (r != 0)
				break;
		}
		Py_DECREF(bases);
		return r;
	}
}

static int
check_class(PyObject *cls, const char *error)
{
	PyObject *bases = abstract_get_bases(cls);
	if (bases == NULL) {
		/* Do not mask errors. */
		if (!PyErr_Occurred())
			PyErr_SetString(PyExc_TypeError, error);
		return 0;
	}
	Py_DECREF(bases);
	return -1;
}

static int
recursive_isinstance(PyObject *inst, PyObject *cls)
{
	PyObject *icls;
	static PyObject *__class__ = NULL;
	int retval = 0;

	if (__class__ == NULL) {
		__class__ = PyUnicode_InternFromString("__class__");
		if (__class__ == NULL)
			return -1;
	}

	if (PyType_Check(cls)) {
		retval = PyObject_TypeCheck(inst, (PyTypeObject *)cls);
		if (retval == 0) {
			PyObject *c = PyObject_GetAttr(inst, __class__);
			if (c == NULL) {
				PyErr_Clear();
			}
			else {
				if (c != (PyObject *)(inst->ob_type) &&
				    PyType_Check(c))
					retval = PyType_IsSubtype(
						(PyTypeObject *)c,
						(PyTypeObject *)cls);
				Py_DECREF(c);
			}
		}
	}
	else {
		if (!check_class(cls,
			"isinstance() arg 2 must be a class, type,"
			" or tuple of classes and types"))
			return -1;
		icls = PyObject_GetAttr(inst, __class__);
		if (icls == NULL) {
			PyErr_Clear();
			retval = 0;
		}
		else {
			retval = abstract_issubclass(icls, cls);
			Py_DECREF(icls);
		}
	}

	return retval;
}

int
PyObject_IsInstance(PyObject *inst, PyObject *cls)
{
	static PyObject *name = NULL;
	PyObject *checker;

	/* Quick test for an exact match */
	if (Py_TYPE(inst) == (PyTypeObject *)cls)
		return 1;

	if (PyTuple_Check(cls)) {
		Py_ssize_t i;
		Py_ssize_t n;
		int r = 0;

		if (Py_EnterRecursiveCall(" in __instancecheck__"))
			return -1;
		n = PyTuple_GET_SIZE(cls);
		for (i = 0; i < n; ++i) {
			PyObject *item = PyTuple_GET_ITEM(cls, i);
			r = PyObject_IsInstance(inst, item);
			if (r != 0)
				/* either found it, or got an error */
				break;
		}
		Py_LeaveRecursiveCall();
		return r;
	}

	checker = _PyObject_LookupSpecial(cls, "__instancecheck__", &name);
	if (checker != NULL) {
		PyObject *res;
		int ok = -1;
		if (Py_EnterRecursiveCall(" in __instancecheck__")) {
			Py_DECREF(checker);
			return ok;
		}
		res = PyObject_CallFunctionObjArgs(checker, inst, NULL);
		Py_LeaveRecursiveCall();
		Py_DECREF(checker);
		if (res != NULL) {
			ok = PyObject_IsTrue(res);
			Py_DECREF(res);
		}
		return ok;
	}
	else if (PyErr_Occurred())
		return -1;
	return recursive_isinstance(inst, cls);
}

static	int
recursive_issubclass(PyObject *derived, PyObject *cls)
{
	if (PyType_Check(cls) && PyType_Check(derived)) {
		/* Fast path (non-recursive) */
		return PyType_IsSubtype((PyTypeObject *)derived, (PyTypeObject *)cls);
	}
	if (!check_class(derived,
			 "issubclass() arg 1 must be a class"))
		return -1;
	if (!check_class(cls,
			"issubclass() arg 2 must be a class"
			" or tuple of classes"))
		return -1;

	return abstract_issubclass(derived, cls);
}

int
PyObject_IsSubclass(PyObject *derived, PyObject *cls)
{
	static PyObject *name = NULL;
	PyObject *checker;

	if (PyTuple_Check(cls)) {
		Py_ssize_t i;
		Py_ssize_t n;
		int r = 0;

		if (Py_EnterRecursiveCall(" in __subclasscheck__"))
			return -1;
		n = PyTuple_GET_SIZE(cls);
		for (i = 0; i < n; ++i) {
			PyObject *item = PyTuple_GET_ITEM(cls, i);
			r = PyObject_IsSubclass(derived, item);
			if (r != 0)
				/* either found it, or got an error */
				break;
		}
		Py_LeaveRecursiveCall();
		return r;
	}

	checker = _PyObject_LookupSpecial(cls, "__subclasscheck__", &name);
	if (checker != NULL) {
		PyObject *res;
		int ok = -1;
		if (Py_EnterRecursiveCall(" in __subclasscheck__")) {
			Py_DECREF(checker);
			return ok;
		}
		res = PyObject_CallFunctionObjArgs(checker, derived, NULL);
		Py_LeaveRecursiveCall();
		Py_DECREF(checker);
		if (res != NULL) {
			ok = PyObject_IsTrue(res);
			Py_DECREF(res);
		}
		return ok;
	}
	else if (PyErr_Occurred())
		return -1;
	return recursive_issubclass(derived, cls);
}

int
_PyObject_RealIsInstance(PyObject *inst, PyObject *cls)
{
	return recursive_isinstance(inst, cls);
}

int
_PyObject_RealIsSubclass(PyObject *derived, PyObject *cls)
{
	return recursive_issubclass(derived, cls);
}


PyObject *
PyObject_GetIter(PyObject *o)
{
	PyTypeObject *t = o->ob_type;
	getiterfunc f = NULL;
	f = t->tp_iter;
	if (f == NULL) {
		if (PySequence_Check(o))
			return PySeqIter_New(o);
		return type_error("'%.200s' object is not iterable", o);
	}
	else {
		PyObject *res = (*f)(o);
		if (res != NULL && !PyIter_Check(res)) {
			PyErr_Format(PyExc_TypeError,
				     "iter() returned non-iterator "
				     "of type '%.100s'",
				     res->ob_type->tp_name);
			Py_DECREF(res);
			res = NULL;
		}
		return res;
	}
}

/* Return next item.
 * If an error occurs, return NULL.  PyErr_Occurred() will be true.
 * If the iteration terminates normally, return NULL and clear the
 * PyExc_StopIteration exception (if it was set).  PyErr_Occurred()
 * will be false.
 * Else return the next object.	 PyErr_Occurred() will be false.
 */
PyObject *
PyIter_Next(PyObject *iter)
{
	PyObject *result;
	result = (*iter->ob_type->tp_iternext)(iter);
	if (result == NULL &&
	    PyErr_Occurred() &&
	    PyErr_ExceptionMatches(PyExc_StopIteration))
		PyErr_Clear();
	return result;
}