Objects/sliceobject.c

   1 /*
   2 Written by Jim Hugunin and Chris Chase.
   3
   4 This includes both the singular ellipsis object and slice objects.
   5
   6 Guido, feel free to do whatever you want in the way of copyrights
   7 for this file.
   8 */
   9
  10 /*
  11 Py_Ellipsis encodes the '...' rubber index token. It is similar to
  12 the Py_NoneStruct in that there is no way to create other objects of
  13 this type and there is exactly one in existence.
  14 */
  15
  16 #include "Python.h"
  17 #include "structmember.h"
  18
  19 static PyObject *
  20 ellipsis_repr(PyObject *op)
  21 {
  22         return PyString_FromString("Ellipsis");
  23 }
  24
  25 static PyTypeObject PyEllipsis_Type = {
  26         PyObject_HEAD_INIT(&PyType_Type)
  27         0,                              /* ob_size */
  28         "ellipsis",                     /* tp_name */
  29         0,                              /* tp_basicsize */
  30         0,                              /* tp_itemsize */
  31         0, /*never called*/             /* tp_dealloc */
  32         0,                              /* tp_print */
  33         0,                              /* tp_getattr */
  34         0,                              /* tp_setattr */
  35         0,                              /* tp_compare */
  36         ellipsis_repr,                  /* tp_repr */
  37         0,                              /* tp_as_number */
  38         0,                              /* tp_as_sequence */
  39         0,                              /* tp_as_mapping */
  40         0,                              /* tp_hash */
  41         0,                              /* tp_call */
  42         0,                              /* tp_str */
  43         PyObject_GenericGetAttr,        /* tp_getattro */
  44         0,                              /* tp_setattro */
  45         0,                              /* tp_as_buffer */
  46         Py_TPFLAGS_DEFAULT,             /* tp_flags */
  47 };
  48
  49 PyObject _Py_EllipsisObject = {
  50         PyObject_HEAD_INIT(&PyEllipsis_Type)
  51 };
  52
  53
  54 /* Slice object implementation
  55
  56    start, stop, and step are python objects with None indicating no
  57    index is present.
  58 */
  59
  60 PyObject *
  61 PySlice_New(PyObject *start, PyObject *stop, PyObject *step)
  62 {
  63         PySliceObject *obj = PyObject_New(PySliceObject, &PySlice_Type);
  64
  65         if (obj == NULL)
  66                 return NULL;
  67
  68         if (step == NULL) step = Py_None;
  69         Py_INCREF(step);
  70         if (start == NULL) start = Py_None;
  71         Py_INCREF(start);
  72         if (stop == NULL) stop = Py_None;
  73         Py_INCREF(stop);
  74
  75         obj->step = step;
  76         obj->start = start;
  77         obj->stop = stop;
  78
  79         return (PyObject *) obj;
  80 }
  81
  82 PyObject *
  83 _PySlice_FromIndices(Py_ssize_t istart, Py_ssize_t istop)
  84 {
  85         PyObject *start, *end, *slice;
  86         start = PyInt_FromSsize_t(istart);
  87         if (!start)
  88                 return NULL;
  89         end = PyInt_FromSsize_t(istop);
  90         if (!end) {
  91                 Py_DECREF(start);
  92                 return NULL;
  93         }
  94
  95         slice = PySlice_New(start, end, NULL);
  96         Py_DECREF(start);
  97         Py_DECREF(end);
  98         return slice;
  99 }
 100
 101 int
 102 PySlice_GetIndices(PySliceObject *r, Py_ssize_t length,
 103                    Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step)
 104 {
 105         /* XXX support long ints */
 106         if (r->step == Py_None) {
 107                 *step = 1;
 108         } else {
 109                 if (!PyInt_Check(r->step) && !PyLong_Check(r->step)) return -1;
 110                 *step = PyInt_AsSsize_t(r->step);
 111         }
 112         if (r->start == Py_None) {
 113                 *start = *step < 0 ? length-1 : 0;
 114         } else {
 115                 if (!PyInt_Check(r->start) && !PyLong_Check(r->step)) return -1;
 116                 *start = PyInt_AsSsize_t(r->start);
 117                 if (*start < 0) *start += length;
 118         }
 119         if (r->stop == Py_None) {
 120                 *stop = *step < 0 ? -1 : length;
 121         } else {
 122                 if (!PyInt_Check(r->stop) && !PyLong_Check(r->step)) return -1;
 123                 *stop = PyInt_AsSsize_t(r->stop);
 124                 if (*stop < 0) *stop += length;
 125         }
 126         if (*stop > length) return -1;
 127         if (*start >= length) return -1;
 128         if (*step == 0) return -1;
 129         return 0;
 130 }
 131
 132 int
 133 PySlice_GetIndicesEx(PySliceObject *r, Py_ssize_t length,
 134                      Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step, Py_ssize_t *slicelength)
 135 {
 136         /* this is harder to get right than you might think */
 137
 138         Py_ssize_t defstart, defstop;
 139
 140         if (r->step == Py_None) {
 141                 *step = 1;
 142         }
 143         else {
 144                 if (!_PyEval_SliceIndex(r->step, step)) return -1;
 145                 if (*step == 0) {
 146                         PyErr_SetString(PyExc_ValueError,
 147                                         "slice step cannot be zero");
 148                         return -1;
 149                 }
 150         }
 151
 152         defstart = *step < 0 ? length-1 : 0;
 153         defstop = *step < 0 ? -1 : length;
 154
 155         if (r->start == Py_None) {
 156                 *start = defstart;
 157         }
 158         else {
 159                 if (!_PyEval_SliceIndex(r->start, start)) return -1;
 160                 if (*start < 0) *start += length;
 161                 if (*start < 0) *start = (*step < 0) ? -1 : 0;
 162                 if (*start >= length)
 163                         *start = (*step < 0) ? length - 1 : length;
 164         }
 165
 166         if (r->stop == Py_None) {
 167                 *stop = defstop;
 168         }
 169         else {
 170                 if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
 171                 if (*stop < 0) *stop += length;
 172                 if (*stop < 0) *stop = -1;
 173                 if (*stop > length) *stop = length;
 174         }
 175
 176         if ((*step < 0 && *stop >= *start)
 177             || (*step > 0 && *start >= *stop)) {
 178                 *slicelength = 0;
 179         }
 180         else if (*step < 0) {
 181                 *slicelength = (*stop-*start+1)/(*step)+1;
 182         }
 183         else {
 184                 *slicelength = (*stop-*start-1)/(*step)+1;
 185         }
 186
 187         return 0;
 188 }
 189
 190 static PyObject *
 191 slice_new(PyTypeObject *type, PyObject *args, PyObject *kw)
 192 {
 193         PyObject *start, *stop, *step;
 194
 195         start = stop = step = NULL;
 196
 197         if (!_PyArg_NoKeywords("slice()", kw))
 198                 return NULL;
 199
 200         if (!PyArg_UnpackTuple(args, "slice", 1, 3, &start, &stop, &step))
 201                 return NULL;
 202
 203         /* This swapping of stop and start is to maintain similarity with
 204            range(). */
 205         if (stop == NULL) {
 206                 stop = start;
 207                 start = NULL;
 208         }
 209         return PySlice_New(start, stop, step);
 210 }
 211
 212 PyDoc_STRVAR(slice_doc,
 213 "slice([start,] stop[, step])\n\
 214 \n\
 215 Create a slice object.  This is used for extended slicing (e.g. a[0:10:2]).");
 216
 217 static void
 218 slice_dealloc(PySliceObject *r)
 219 {
 220         Py_DECREF(r->step);
 221         Py_DECREF(r->start);
 222         Py_DECREF(r->stop);
 223         PyObject_Del(r);
 224 }
 225
 226 static PyObject *
 227 slice_repr(PySliceObject *r)
 228 {
 229         PyObject *s, *comma;
 230
 231         s = PyString_FromString("slice(");
 232         comma = PyString_FromString(", ");
 233         PyString_ConcatAndDel(&s, PyObject_Repr(r->start));
 234         PyString_Concat(&s, comma);
 235         PyString_ConcatAndDel(&s, PyObject_Repr(r->stop));
 236         PyString_Concat(&s, comma);
 237         PyString_ConcatAndDel(&s, PyObject_Repr(r->step));
 238         PyString_ConcatAndDel(&s, PyString_FromString(")"));
 239         Py_DECREF(comma);
 240         return s;
 241 }
 242
 243 static PyMemberDef slice_members[] = {
 244         {"start", T_OBJECT, offsetof(PySliceObject, start), READONLY},
 245         {"stop", T_OBJECT, offsetof(PySliceObject, stop), READONLY},
 246         {"step", T_OBJECT, offsetof(PySliceObject, step), READONLY},
 247         {0}
 248 };
 249
 250 static PyObject*
 251 slice_indices(PySliceObject* self, PyObject* len)
 252 {
 253         Py_ssize_t ilen, start, stop, step, slicelength;
 254
 255         ilen = PyInt_AsSsize_t(len);
 256
 257         if (ilen == -1 && PyErr_Occurred()) {
 258                 return NULL;
 259         }
 260
 261         if (PySlice_GetIndicesEx(self, ilen, &start, &stop,
 262                                  &step, &slicelength) < 0) {
 263                 return NULL;
 264         }
 265
 266         return Py_BuildValue("(nnn)", start, stop, step);
 267 }
 268
 269 PyDoc_STRVAR(slice_indices_doc,
 270 "S.indices(len) -> (start, stop, stride)\n\
 271 \n\
 272 Assuming a sequence of length len, calculate the start and stop\n\
 273 indices, and the stride length of the extended slice described by\n\
 274 S. Out of bounds indices are clipped in a manner consistent with the\n\
 275 handling of normal slices.");
 276
 277 static PyMethodDef slice_methods[] = {
 278         {"indices",     (PyCFunction)slice_indices,
 279          METH_O,        slice_indices_doc},
 280         {NULL, NULL}
 281 };
 282
 283 static int
 284 slice_compare(PySliceObject *v, PySliceObject *w)
 285 {
 286         int result = 0;
 287
 288         if (v == w)
 289                 return 0;
 290
 291         if (PyObject_Cmp(v->start, w->start, &result) < 0)
 292             return -2;
 293         if (result != 0)
 294                 return result;
 295         if (PyObject_Cmp(v->stop, w->stop, &result) < 0)
 296             return -2;
 297         if (result != 0)
 298                 return result;
 299         if (PyObject_Cmp(v->step, w->step, &result) < 0)
 300             return -2;
 301         return result;
 302 }
 303
 304 static long
 305 slice_hash(PySliceObject *v)
 306 {
 307         PyErr_SetString(PyExc_TypeError, "unhashable type");
 308         return -1L;
 309 }
 310
 311 PyTypeObject PySlice_Type = {
 312         PyObject_HEAD_INIT(&PyType_Type)
 313         0,                      /* Number of items for varobject */
 314         "slice",                /* Name of this type */
 315         sizeof(PySliceObject),  /* Basic object size */
 316         0,                      /* Item size for varobject */
 317         (destructor)slice_dealloc,              /* tp_dealloc */
 318         0,                                      /* tp_print */
 319         0,                                      /* tp_getattr */
 320         0,                                      /* tp_setattr */
 321         (cmpfunc)slice_compare,                 /* tp_compare */
 322         (reprfunc)slice_repr,                   /* tp_repr */
 323         0,                                      /* tp_as_number */
 324         0,                                      /* tp_as_sequence */
 325         0,                                      /* tp_as_mapping */
 326         (hashfunc)slice_hash,                   /* tp_hash */
 327         0,                                      /* tp_call */
 328         0,                                      /* tp_str */
 329         PyObject_GenericGetAttr,                /* tp_getattro */
 330         0,                                      /* tp_setattro */
 331         0,                                      /* tp_as_buffer */
 332         Py_TPFLAGS_DEFAULT,                     /* tp_flags */
 333         slice_doc,                              /* tp_doc */
 334         0,                                      /* tp_traverse */
 335         0,                                      /* tp_clear */
 336         0,                                      /* tp_richcompare */
 337         0,                                      /* tp_weaklistoffset */
 338         0,                                      /* tp_iter */
 339         0,                                      /* tp_iternext */
 340         slice_methods,                          /* tp_methods */
 341         slice_members,                          /* tp_members */
 342         0,                                      /* tp_getset */
 343         0,                                      /* tp_base */
 344         0,                                      /* tp_dict */
 345         0,                                      /* tp_descr_get */
 346         0,                                      /* tp_descr_set */
 347         0,                                      /* tp_dictoffset */
 348         0,                                      /* tp_init */
 349         0,                                      /* tp_alloc */
 350         slice_new,                              /* tp_new */
 351 };