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Tidied up the implementations of reversed (including the custom ones

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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.
This commit is contained in:
Raymond Hettinger 2004-03-10 10:10:42 +00:00
parent d2c36261a2
commit ef9bf4031a
4 changed files with 59 additions and 29 deletions
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34
Objects/listobject.c
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@ -2793,21 +2793,35 @@ listreviter_traverse(listreviterobject *it, visitproc visit, void *arg)
static PyObject *
listreviter_next(listreviterobject *it)
{
PyObject *item = NULL;
PyObject *item;
long index = it->it_index;
PyListObject *seq = it->it_seq;
assert(PyList_Check(it->it_seq));
if (it->it_index >= 0) {
assert(it->it_index < PyList_GET_SIZE(it->it_seq));
item = PyList_GET_ITEM(it->it_seq, it->it_index);
if (index>=0 && index < PyList_GET_SIZE(seq)) {
item = PyList_GET_ITEM(seq, index);
it->it_index--;
Py_INCREF(item);
} else if (it->it_seq != NULL) {
Py_DECREF(it->it_seq);
it->it_seq = NULL;
return item;
}
return item;
it->it_index = -1;
if (seq != NULL) {
it->it_seq = NULL;
Py_DECREF(seq);
}
return NULL;
}
static int
listreviter_len(listreviterobject *it)
{
return it->it_index + 1;
}
static PySequenceMethods listreviter_as_sequence = {
(inquiry)listreviter_len, /* sq_length */
0, /* sq_concat */
};
PyTypeObject PyListRevIter_Type = {
PyObject_HEAD_INIT(&PyType_Type)
0, /* ob_size */
@ -2822,7 +2836,7 @@ PyTypeObject PyListRevIter_Type = {
0, /* tp_compare */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
&listreviter_as_sequence, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */