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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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36
Objects/enumobject.c
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@ -217,23 +217,21 @@ static PyObject *
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 @@ PyDoc_STRVAR(reversed_doc,
"\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 */