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Some days, I think my comment of 

/* this is harder to get right than you might think */

angered some God somewhere.  After noticing

    >>> range(5000000)[slice(96360, None, 439)]
    []

I found that my cute test for the slice being empty failed due to
overflow.  Fixed, and added simple test (not the above!).
This commit is contained in:
Michael W. Hudson 2002-11-05 15:28:51 +00:00
parent d7c14c6c9b
commit 173f11da5d
2 changed files with 15 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Lib/test/test_slice.py
View File

@ -1,6 +1,7 @@
# tests for slice objects; in particular the indices method. # tests for slice objects; in particular the indices method.
from test.test_support import vereq from test.test_support import vereq
import sys
vereq(slice(None ).indices(10), (0, 10, 1)) vereq(slice(None ).indices(10), (0, 10, 1))
vereq(slice(None, None, 2).indices(10), (0, 10, 2)) vereq(slice(None, None, 2).indices(10), (0, 10, 2))
@ -11,3 +12,5 @@
vereq(slice(-100, 100 ).indices(10), slice(None).indices(10)) vereq(slice(-100, 100 ).indices(10), slice(None).indices(10))
vereq(slice(100, -100, -1).indices(10), slice(None, None, -1).indices(10)) vereq(slice(100, -100, -1).indices(10), slice(None, None, -1).indices(10))
vereq(slice(-100L, 100L, 2L).indices(10), (0, 10, 2)) vereq(slice(-100L, 100L, 2L).indices(10), (0, 10, 2))
vereq(range(10)[::sys.maxint - 1], [0])

18
Objects/sliceobject.c
View File

@ -114,11 +114,13 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
int *start, int *stop, int *step, int *slicelength) int *start, int *stop, int *step, int *slicelength)
{ {
/* this is harder to get right than you might think */ /* this is harder to get right than you might think */
int defstart, defstop; int defstart, defstop;
if (r->step == Py_None) { if (r->step == Py_None) {
*step = 1; *step = 1;
} else { }
else {
*step = PyInt_AsLong(r->step); *step = PyInt_AsLong(r->step);
if (*step == -1 && PyErr_Occurred()) { if (*step == -1 && PyErr_Occurred()) {
return -1; return -1;
@ -135,7 +137,8 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
if (r->start == Py_None) { if (r->start == Py_None) {
*start = defstart; *start = defstart;
} else { }
else {
if (!_PyEval_SliceIndex(r->start, start)) return -1; if (!_PyEval_SliceIndex(r->start, start)) return -1;
if (*start < 0) *start += length; if (*start < 0) *start += length;
if (*start < 0) *start = (*step < 0) ? -1 : 0; if (*start < 0) *start = (*step < 0) ? -1 : 0;
@ -145,19 +148,22 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
if (r->stop == Py_None) { if (r->stop == Py_None) {
*stop = defstop; *stop = defstop;
} else { }
else {
if (!_PyEval_SliceIndex(r->stop, stop)) return -1; if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
if (*stop < 0) *stop += length; if (*stop < 0) *stop += length;
if (*stop < 0) *stop = -1; if (*stop < 0) *stop = -1;
if (*stop > length) *stop = length; if (*stop > length) *stop = length;
} }
if ((*stop - *start)*(*step) <= 0) { if ((*step < 0 && *stop >= *start)
|| (*step > 0 && *start >= *stop)) {
*slicelength = 0; *slicelength = 0;
} }
else if (*step < 0) { else if (*step < 0) {
*slicelength = (*stop-*start+1)/(*step)+1; *slicelength = (*stop-*start+1)/(*step)+1;
} else { }
else {
*slicelength = (*stop-*start-1)/(*step)+1; *slicelength = (*stop-*start-1)/(*step)+1;
} }