Generalize list(seq) to work with iterators. This also generalizes list()
to no longer insist that len(seq) be defined.
NEEDS DOC CHANGES.
This is meant to be a model for how other functions of this ilk (max,
filter, etc) can be generalized similarly. Feel encouraged to grab your
favorite and convert it!
Note some cute consequences:
list(file) == file.readlines() == list(file.xreadlines())
list(dict) == dict.keys()
list(dict.iteritems()) = dict.items()
list(xrange(i, j, k)) == range(i, j, k)
diff --git a/Objects/abstract.c b/Objects/abstract.c
index f656747..a5f97a1 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -1236,52 +1236,78 @@
PyObject *
PySequence_List(PyObject *v)
{
- PySequenceMethods *m;
+ PyObject *it; /* iter(v) */
+ PyObject *result; /* result list */
+ int n; /* guess for result list size */
+ int i;
if (v == NULL)
return null_error();
+ /* Special-case list(a_list), for speed. */
if (PyList_Check(v))
return PyList_GetSlice(v, 0, PyList_GET_SIZE(v));
- m = v->ob_type->tp_as_sequence;
- if (m && m->sq_item) {
- int i;
- PyObject *l;
- int n = PySequence_Size(v);
+ /* Get iterator. There may be some low-level efficiency to be gained
+ * by caching the tp_iternext slot instead of using PyIter_Next()
+ * later, but premature optimization is the root etc.
+ */
+ it = PyObject_GetIter(v);
+ if (it == NULL)
+ return NULL;
+
+ /* Guess a result list size. */
+ n = -1; /* unknown */
+ if (PySequence_Check(v) &&
+ v->ob_type->tp_as_sequence->sq_length) {
+ n = PySequence_Size(v);
if (n < 0)
- return NULL;
- l = PyList_New(n);
- if (l == NULL)
- return NULL;
- for (i = 0; ; i++) {
- PyObject *item = (*m->sq_item)(v, i);
- if (item == NULL) {
- if (PyErr_ExceptionMatches(PyExc_IndexError))
+ PyErr_Clear();
+ }
+ if (n < 0)
+ n = 8; /* arbitrary */
+ result = PyList_New(n);
+ if (result == NULL) {
+ Py_DECREF(it);
+ return NULL;
+ }
+
+ /* Run iterator to exhaustion. */
+ for (i = 0; ; i++) {
+ PyObject *item = PyIter_Next(it);
+ if (item == NULL) {
+ /* We're out of here in any case, but if this is a
+ * StopIteration exception it's expected, but if
+ * any other kind of exception it's an error.
+ */
+ if (PyErr_Occurred()) {
+ if (PyErr_ExceptionMatches(PyExc_StopIteration))
PyErr_Clear();
else {
- Py_DECREF(l);
- l = NULL;
+ Py_DECREF(result);
+ result = NULL;
}
- break;
}
- if (i < n)
- PyList_SET_ITEM(l, i, item);
- else if (PyList_Append(l, item) < 0) {
- Py_DECREF(l);
- l = NULL;
- break;
- }
+ break;
}
- if (i < n && l != NULL) {
- if (PyList_SetSlice(l, i, n, (PyObject *)NULL) != 0) {
- Py_DECREF(l);
- l = NULL;
- }
+ if (i < n)
+ PyList_SET_ITEM(result, i, item);
+ else if (PyList_Append(result, item) < 0) {
+ Py_DECREF(result);
+ result = NULL;
+ break;
}
- return l;
}
- return type_error("list() argument must be a sequence");
+
+ /* Cut back result list if initial guess was too large. */
+ if (i < n && result != NULL) {
+ if (PyList_SetSlice(result, i, n, (PyObject *)NULL) != 0) {
+ Py_DECREF(result);
+ result = NULL;
+ }
+ }
+ Py_DECREF(it);
+ return result;
}
PyObject *