cpython/Objects/sliceobject.c

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/*
Written by Jim Hugunin and Chris Chase.
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.
*/
/*
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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{
return PyString_FromString("Ellipsis");
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}
static PyTypeObject PyEllipsis_Type = {
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PyObject_HEAD_INIT(&PyType_Type)
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 */
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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};
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;
}
PyObject *
_PySlice_FromIndices(Py_ssize_t istart, Py_ssize_t istop)
{
PyObject *start, *end, *slice;
start = PyInt_FromSsize_t(istart);
if (!start)
return NULL;
end = PyInt_FromSsize_t(istop);
if (!end) {
Py_DECREF(start);
return NULL;
}
slice = PySlice_New(start, end, NULL);
Py_DECREF(start);
Py_DECREF(end);
return slice;
}
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int
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PySlice_GetIndices(PySliceObject *r, Py_ssize_t length,
Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step)
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{
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/* XXX support long ints */
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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;
}
int
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PySlice_GetIndicesEx(PySliceObject *r, Py_ssize_t length,
Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step, Py_ssize_t *slicelength)
{
/* this is harder to get right than you might think */
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Py_ssize_t defstart, defstop;
if (r->step == Py_None) {
*step = 1;
}
else {
if (!_PyEval_SliceIndex(r->step, step)) return -1;
if (*step == 0) {
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;
}
else {
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;
}
else {
if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
if (*stop < 0) *stop += length;
if (*stop < 0) *stop = -1;
if (*stop > length) *stop = length;
}
if ((*step < 0 && *stop >= *start)
|| (*step > 0 && *start >= *stop)) {
*slicelength = 0;
}
else if (*step < 0) {
*slicelength = (*stop-*start+1)/(*step)+1;
}
else {
*slicelength = (*stop-*start-1)/(*step)+1;
}
return 0;
}
static PyObject *
slice_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
PyObject *start, *stop, *step;
start = stop = step = NULL;
if (!_PyArg_NoKeywords("slice()", kw))
return NULL;
if (!PyArg_UnpackTuple(args, "slice", 1, 3, &start, &stop, &step))
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;
}
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)
{
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Py_ssize_t 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);
}
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,
METH_O, slice_indices_doc},
{NULL, NULL}
};
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 */
(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 */
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 */
slice_methods, /* tp_methods */
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slice_members, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
0, /* tp_alloc */
slice_new, /* tp_new */
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};