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.

1 files changed, 13 insertions, 1 deletions

diff --git a/Objects/rangeobject.c b/Objects/rangeobject.c
index 1f56728..a6d1611 100644
--- a/Objects/rangeobject.c
+++ b/Objects/rangeobject.c
@@ -288,6 +288,18 @@ rangeiter_next(rangeiterobject *r)
 	return NULL;
 }
 
+static int
+rangeiter_len(rangeiterobject *r)
+{
+	return r->len - r->index;
+}
+
+static PySequenceMethods rangeiter_as_sequence = {
+	(inquiry)rangeiter_len,		/* sq_length */
+	0,				/* sq_concat */
+};
+
+
 static PyTypeObject Pyrangeiter_Type = {
 	PyObject_HEAD_INIT(&PyType_Type)
 	0,                                      /* ob_size */
@@ -302,7 +314,7 @@ static PyTypeObject Pyrangeiter_Type = {
 	0,                                      /* tp_compare */
 	0,                                      /* tp_repr */
 	0,                                      /* tp_as_number */
-	0,                                      /* tp_as_sequence */
+	&rangeiter_as_sequence,			/* tp_as_sequence */
 	0,                                      /* tp_as_mapping */
 	0,                                      /* tp_hash */
 	0,                                      /* tp_call */