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Improve extended slicing support in builtin types and classes. Specifically:

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- Specialcase extended slices that amount to a shallow copy the same way as
   is done for simple slices, in the tuple, string and unicode case.

 - Specialcase step-1 extended slices to optimize the common case for all
   involved types.

 - For lists, allow extended slice assignment of differing lengths as long
   as the step is 1. (Previously, 'l[:2:1] = []' failed even though
   'l[:2] = []' and 'l[:2:None] = []' do not.)

 - Implement extended slicing for buffer, array, structseq, mmap and
   UserString.UserString.

 - Implement slice-object support (but not non-step-1 slice assignment) for
   UserString.MutableString.

 - Add tests for all new functionality.
This commit is contained in:
Thomas Wouters 2007-08-28 15:28:19 +00:00
parent 0f4a14b56f
commit 3ccec68a05
16 changed files with 730 additions and 120 deletions
Download patch file Download diff file Expand all files Collapse all files

43
Objects/listobject.c
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@ -2473,6 +2473,9 @@ list_subscript(PyListObject* self, PyObject* item)
if (slicelength <= 0) {
return PyList_New(0);
}
else if (step == 1) {
return list_slice(self, start, stop);
}
else {
result = PyList_New(slicelength);
if (!result) return NULL;
@ -2516,10 +2519,15 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
return -1;
}
/* treat L[slice(a,b)] = v _exactly_ like L[a:b] = v */
if (step == 1 && ((PySliceObject*)item)->step == Py_None)
if (step == 1)
return list_ass_slice(self, start, stop, value);
/* Make sure s[5:2] = [..] inserts at the right place:
before 5, not before 2. */
if ((step < 0 && start < stop) ||
(step > 0 && start > stop))
stop = start;
if (value == NULL) {
/* delete slice */
PyObject **garbage;
@ -2541,12 +2549,16 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
return -1;
}
/* drawing pictures might help
understand these for loops */
/* drawing pictures might help understand these for
loops. Basically, we memmove the parts of the
list that are *not* part of the slice: step-1
items for each item that is part of the slice,
and then tail end of the list that was not
covered by the slice */
for (cur = start, i = 0;
cur < stop;
cur += step, i++) {
Py_ssize_t lim = step;
Py_ssize_t lim = step - 1;
garbage[i] = PyList_GET_ITEM(self, cur);
@ -2558,11 +2570,12 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
self->ob_item + cur + 1,
lim * sizeof(PyObject *));
}
for (cur = start + slicelength*step + 1;
cur < Py_Size(self); cur++) {
PyList_SET_ITEM(self, cur - slicelength,
PyList_GET_ITEM(self, cur));
cur = start + slicelength*step;
if (cur < Py_Size(self)) {
memmove(self->ob_item + cur - slicelength,
self->ob_item + cur,
(Py_Size(self) - cur) *
sizeof(PyObject *));
}
Py_Size(self) -= slicelength;
@ -2577,7 +2590,8 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
}
else {
/* assign slice */
PyObject **garbage, *ins, *seq, **seqitems, **selfitems;
PyObject *ins, *seq;
PyObject **garbage, **seqitems, **selfitems;
Py_ssize_t cur, i;
/* protect against a[::-1] = a */
@ -2587,14 +2601,17 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
}
else {
seq = PySequence_Fast(value,
"must assign iterable to extended slice");
"must assign iterable "
"to extended slice");
}
if (!seq)
return -1;
if (PySequence_Fast_GET_SIZE(seq) != slicelength) {
PyErr_Format(PyExc_ValueError,
"attempt to assign sequence of size %zd to extended slice of size %zd",
"attempt to assign sequence of "
"size %zd to extended slice of "
"size %zd",
PySequence_Fast_GET_SIZE(seq),
slicelength);
Py_DECREF(seq);