sliceobject.c 7.47 KB
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/*
Written by Jim Hugunin and Chris Chase.

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This includes both the singular ellipsis object and slice objects.
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Guido, feel free to do whatever you want in the way of copyrights
for this file.
*/

/* 
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Py_Ellipsis encodes the '...' rubber index token. It is similar to
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the Py_NoneStruct in that there is no way to create other objects of
this type and there is exactly one in existence.
*/

#include "Python.h"
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#include "structmember.h"
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static PyObject *
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ellipsis_repr(PyObject *op)
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{
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	return PyString_FromString("Ellipsis");
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}

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static PyTypeObject PyEllipsis_Type = {
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	PyObject_HEAD_INIT(&PyType_Type)
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	0,					/* ob_size */
	"ellipsis",				/* tp_name */
	0,					/* tp_basicsize */
	0,					/* tp_itemsize */
	0, /*never called*/			/* tp_dealloc */
	0,					/* tp_print */
	0,					/* tp_getattr */
	0,					/* tp_setattr */
	0,					/* tp_compare */
	(reprfunc)ellipsis_repr,		/* tp_repr */
	0,					/* tp_as_number */
	0,					/* tp_as_sequence */
	0,					/* tp_as_mapping */
	0,					/* tp_hash */
	0,					/* tp_call */
	0,					/* tp_str */
	PyObject_GenericGetAttr,		/* tp_getattro */
	0,					/* tp_setattro */
	0,					/* tp_as_buffer */
	Py_TPFLAGS_DEFAULT,			/* tp_flags */
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};

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PyObject _Py_EllipsisObject = {
	PyObject_HEAD_INIT(&PyEllipsis_Type)
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};


/* Slice object implementation

   start, stop, and step are python objects with None indicating no
   index is present.
*/

PyObject *
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PySlice_New(PyObject *start, PyObject *stop, PyObject *step)
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{
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	PySliceObject *obj = PyObject_New(PySliceObject, &PySlice_Type);
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	if (obj == NULL)
		return NULL;

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	if (step == NULL) step = Py_None;
	Py_INCREF(step);
	if (start == NULL) start = Py_None;
	Py_INCREF(start);
	if (stop == NULL) stop = Py_None;
	Py_INCREF(stop);

	obj->step = step;
	obj->start = start;
	obj->stop = stop;

	return (PyObject *) obj;
}

int
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PySlice_GetIndices(PySliceObject *r, int length,
                   int *start, int *stop, int *step)
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{
	if (r->step == Py_None) {
		*step = 1;
	} else {
		if (!PyInt_Check(r->step)) return -1;
		*step = PyInt_AsLong(r->step);
	}
	if (r->start == Py_None) {
		*start = *step < 0 ? length-1 : 0;
	} else {
		if (!PyInt_Check(r->start)) return -1;
		*start = PyInt_AsLong(r->start);
		if (*start < 0) *start += length;
	}
	if (r->stop == Py_None) {
		*stop = *step < 0 ? -1 : length;
	} else {
		if (!PyInt_Check(r->stop)) return -1;
		*stop = PyInt_AsLong(r->stop);
		if (*stop < 0) *stop += length;
	}
	if (*stop > length) return -1;
	if (*start >= length) return -1;
	if (*step == 0) return -1;
	return 0;
}

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int
PySlice_GetIndicesEx(PySliceObject *r, int length,
		     int *start, int *stop, int *step, int *slicelength)
{
	/* this is harder to get right than you might think */
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	int defstart, defstop;

	if (r->step == Py_None) {
		*step = 1;
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	} 
	else {
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		if (!_PyEval_SliceIndex(r->step, step)) return -1;
		if (*step == 0) {
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			PyErr_SetString(PyExc_ValueError,
					"slice step cannot be zero");
			return -1;
		}
	}

	defstart = *step < 0 ? length-1 : 0;
	defstop = *step < 0 ? -1 : length;

	if (r->start == Py_None) {
		*start = defstart;
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	}
	else {
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		if (!_PyEval_SliceIndex(r->start, start)) return -1;
		if (*start < 0) *start += length;
		if (*start < 0) *start = (*step < 0) ? -1 : 0;
		if (*start >= length) 
			*start = (*step < 0) ? length - 1 : length;
	}

	if (r->stop == Py_None) {
		*stop = defstop;
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	}
	else {
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		if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
		if (*stop < 0) *stop += length;
		if (*stop < 0) *stop = -1;
		if (*stop > length) *stop = length;
	}
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	if ((*step < 0 && *stop >= *start) 
	    || (*step > 0 && *start >= *stop)) {
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		*slicelength = 0;
	}
	else if (*step < 0) {
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		*slicelength = (*stop-*start+1)/(*step)+1;
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	}
	else {
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		*slicelength = (*stop-*start-1)/(*step)+1;
	}

	return 0;
}

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static PyObject *
slice_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
	PyObject *start, *stop, *step;

	start = stop = step = NULL;

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	if (!PyArg_UnpackTuple(args, "slice", 1, 3, &start, &stop, &step))
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		return NULL;

	/* This swapping of stop and start is to maintain similarity with
	   range(). */
	if (stop == NULL) {
		stop = start;
		start = NULL;
	}
	return PySlice_New(start, stop, step);
}

PyDoc_STRVAR(slice_doc,
"slice([start,] stop[, step])\n\
\n\
Create a slice object.  This is used for extended slicing (e.g. a[0:10:2]).");

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static void
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slice_dealloc(PySliceObject *r)
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{
	Py_DECREF(r->step);
	Py_DECREF(r->start);
	Py_DECREF(r->stop);
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	PyObject_Del(r);
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}

static PyObject *
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slice_repr(PySliceObject *r)
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{
	PyObject *s, *comma;

	s = PyString_FromString("slice(");
	comma = PyString_FromString(", ");
	PyString_ConcatAndDel(&s, PyObject_Repr(r->start));
	PyString_Concat(&s, comma);
	PyString_ConcatAndDel(&s, PyObject_Repr(r->stop));
	PyString_Concat(&s, comma);
	PyString_ConcatAndDel(&s, PyObject_Repr(r->step));
	PyString_ConcatAndDel(&s, PyString_FromString(")"));
	Py_DECREF(comma);
	return s;
}

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static PyMemberDef slice_members[] = {
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	{"start", T_OBJECT, offsetof(PySliceObject, start), READONLY},
	{"stop", T_OBJECT, offsetof(PySliceObject, stop), READONLY},
	{"step", T_OBJECT, offsetof(PySliceObject, step), READONLY},
	{0}
};
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static PyObject*
slice_indices(PySliceObject* self, PyObject* len)
{
	int ilen, start, stop, step, slicelength;

	ilen = PyInt_AsLong(len);

	if (ilen == -1 && PyErr_Occurred()) {
		return NULL;
	}

	if (PySlice_GetIndicesEx(self, ilen, &start, &stop, 
				 &step, &slicelength) < 0) {
		return NULL;
	}

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	return Py_BuildValue("(iii)", start, stop, step);
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}

PyDoc_STRVAR(slice_indices_doc,
"S.indices(len) -> (start, stop, stride)\n\
\n\
Assuming a sequence of length len, calculate the start and stop\n\
indices, and the stride length of the extended slice described by\n\
S. Out of bounds indices are clipped in a manner consistent with the\n\
handling of normal slices.");

static PyMethodDef slice_methods[] = {
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	{"indices",	(PyCFunction)slice_indices,
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	 METH_O,	slice_indices_doc},
	{NULL, NULL}
};

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static int
slice_compare(PySliceObject *v, PySliceObject *w)
{
	int result = 0;

        if (v == w)
		return 0;

	if (PyObject_Cmp(v->start, w->start, &result) < 0)
	    return -2;
	if (result != 0)
		return result;
	if (PyObject_Cmp(v->stop, w->stop, &result) < 0)
	    return -2;
	if (result != 0)
		return result;
	if (PyObject_Cmp(v->step, w->step, &result) < 0)
	    return -2;
	return result;
}
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static long
slice_hash(PySliceObject *v)
{
	PyErr_SetString(PyExc_TypeError, "unhashable type");
	return -1L;
}

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PyTypeObject PySlice_Type = {
	PyObject_HEAD_INIT(&PyType_Type)
	0,			/* Number of items for varobject */
	"slice",		/* Name of this type */
	sizeof(PySliceObject),	/* Basic object size */
	0,			/* Item size for varobject */
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	(destructor)slice_dealloc,		/* tp_dealloc */
	0,					/* tp_print */
	0,					/* tp_getattr */
	0,					/* tp_setattr */
	(cmpfunc)slice_compare, 		/* tp_compare */
	(reprfunc)slice_repr,   		/* tp_repr */
	0,					/* tp_as_number */
	0,	    				/* tp_as_sequence */
	0,					/* tp_as_mapping */
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	(hashfunc)slice_hash,			/* tp_hash */
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	0,					/* tp_call */
	0,					/* tp_str */
	PyObject_GenericGetAttr,		/* tp_getattro */
	0,					/* tp_setattro */
	0,					/* tp_as_buffer */
	Py_TPFLAGS_DEFAULT,			/* tp_flags */
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	slice_doc,				/* tp_doc */
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	0,					/* tp_traverse */
	0,					/* tp_clear */
	0,					/* tp_richcompare */
	0,					/* tp_weaklistoffset */
	0,					/* tp_iter */
	0,					/* tp_iternext */
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	slice_methods,				/* tp_methods */
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	slice_members,				/* tp_members */
	0,					/* tp_getset */
	0,					/* tp_base */
	0,					/* tp_dict */
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	0,					/* tp_descr_get */
	0,					/* tp_descr_set */
	0,					/* tp_dictoffset */
	0,					/* tp_init */
	0,					/* tp_alloc */
	slice_new,				/* tp_new */
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};