Tidied up the implementations of reversed (including the custom ones
for xrange and list objects).
* list.__reversed__ now checks the length of the sequence object before
calling PyList_GET_ITEM() because the mutable could have changed length.
* all three implementations are now tranparent with respect to length and
maintain the invariant len(it) == len(list(it)) even when the underlying
sequence mutates.
* __builtin__.reversed() now frees the underlying sequence as soon
as the iterator is exhausted.
* the code paths were rearranged so that the most common paths
do not require a jump.
diff --git a/Objects/enumobject.c b/Objects/enumobject.c
index 1d13123..28719a9 100644
--- a/Objects/enumobject.c
+++ b/Objects/enumobject.c
@@ -217,23 +217,21 @@
reversed_next(reversedobject *ro)
{
PyObject *item;
+ long index = ro->index;
- if (ro->index < 0)
- return NULL;
-
- assert(PySequence_Check(ro->seq));
- item = PySequence_GetItem(ro->seq, ro->index);
- if (item == NULL)
- return NULL;
-
- ro->index--;
- return item;
-}
-
-static int
-reversed_len(reversedobject *ro)
-{
- return PyObject_Size(ro->seq);
+ if (index >= 0) {
+ item = PySequence_GetItem(ro->seq, index);
+ if (item != NULL) {
+ ro->index--;
+ return item;
+ }
+ }
+ ro->index = -1;
+ if (ro->seq != NULL) {
+ Py_DECREF(ro->seq);
+ ro->seq = NULL;
+ }
+ return NULL;
}
PyDoc_STRVAR(reversed_doc,
@@ -241,6 +239,12 @@
"\n"
"Return a reverse iterator");
+static int
+reversed_len(reversedobject *ro)
+{
+ return ro->index + 1;
+}
+
static PySequenceMethods reversed_as_sequence = {
(inquiry)reversed_len, /* sq_length */
0, /* sq_concat */