This is a reorganization of list_ass_slice(). It should probably be reviewed,

though I tried to be very careful.  This is a slight simplification, and it
adds a new feature: a small stack-allocated "recycled" array for the cases
when we don't remove too many items.

It allows PyList_SetSlice() to never fail if:
* you are sure that the object is a list; and
* you either do not remove more than 8 items, or clear the list.

This makes a number of other places in the source code correct again -- there
are some places that delete a single item without checking for MemoryErrors
raised by PyList_SetSlice(), or that clear the whole list, and sometimes the
context doesn't allow an error to be propagated.

diff --git a/Objects/listobject.c b/Objects/listobject.c
index bd5b95a33c29fcbb4d3b746f1727c7fdefd8ff48..2adc4f45269ef57b3719298c93d73efa54db7ec5 100644 (file)
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -517,6 +517,7 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
           we temporarily copy the items that are deleted from the
           list. :-( */
        PyObject **recycle, **p;
+       PyObject *recycled[8];
        PyObject **item;
        PyObject **vitem = NULL;
        PyObject *v_as_SF = NULL; /* PySequence_Fast(v) */
@@ -559,8 +560,10 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
                return list_clear(a);
        }
        item = a->ob_item;
-       if (ihigh > ilow) {
-               p = recycle = PyMem_NEW(PyObject *, (ihigh-ilow));
+       /* recycle the ihigh-ilow items that we are about to remove */
+       s = (ihigh - ilow)*sizeof(PyObject *);
+       if (s > sizeof(recycled)) {
+               recycle = (PyObject **)PyMem_MALLOC(s);
                if (recycle == NULL) {
                        PyErr_NoMemory();
                        Py_XDECREF(v_as_SF);
@@ -568,41 +571,36 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
                }
        }
        else
-               p = recycle = NULL;
-       if (d <= 0) { /* Delete -d items; recycle ihigh-ilow items */
-               memcpy(p, &item[ilow], (ihigh - ilow)*sizeof(PyObject *));
-               p += ihigh - ilow;
-               if (d < 0) {
-                       memmove(&item[ihigh+d], &item[ihigh],
-                               (a->ob_size - ihigh)*sizeof(PyObject *));
-                       list_resize(a, a->ob_size + d);
-                       item = a->ob_item;
-               }
+               recycle = recycled;
+       p = recycle + (ihigh - ilow);
+       memcpy(recycle, &item[ilow], s);
+       if (d < 0) { /* Delete -d items */
+               memmove(&item[ihigh+d], &item[ihigh],
+                       (a->ob_size - ihigh)*sizeof(PyObject *));
+               list_resize(a, a->ob_size + d);
+               item = a->ob_item;
        }
-       else { /* Insert d items; recycle ihigh-ilow items */
+       else if (d > 0) { /* Insert d items */
                s = a->ob_size;
                if (list_resize(a, s+d) == -1) {
-                       if (recycle != NULL)
-                               PyMem_DEL(recycle);
+                       if (recycle != recycled)
+                               PyMem_FREE(recycle);
                        Py_XDECREF(v_as_SF);
                        return -1;
                }
                item = a->ob_item;
                memmove(&item[ihigh+d], &item[ihigh],
                        (s - ihigh)*sizeof(PyObject *));
-               memcpy(p, &item[ilow], (ihigh - ilow)*sizeof(PyObject *));
-               p += ihigh - ilow;
        }
        for (k = 0; k < n; k++, ilow++) {
                PyObject *w = vitem[k];
                Py_XINCREF(w);
                item[ilow] = w;
        }
-       if (recycle) {
-               while (--p >= recycle)
-                       Py_XDECREF(*p);
-               PyMem_DEL(recycle);
-       }
+       while (--p >= recycle)
+               Py_XDECREF(*p);
+       if (recycle != recycled)
+               PyMem_FREE(recycle);
        Py_XDECREF(v_as_SF);
        return 0;
 #undef b