python · methane · Mar 14, 2022 · Mar 8, 2022 · Mar 8, 2022 · Mar 8, 2022
diff --git a/Misc/ACKS b/Misc/ACKS
@@ -1335,6 +1335,7 @@ William Park
 Claude Paroz
 Heikki Partanen
 Harri Pasanen
+Jeremiah Gabriel Pascual
 Gaël Pasgrimaud
 Feanil Patel
 Ashish Nitin Patil
@@ -1863,7 +1864,6 @@ Kurt Vile
 Norman Vine
 Pauli Virtanen
 Frank Visser
-Jeremiah Vivian (Pascual)
 Johannes Vogel
 Michael Vogt
 Radu Voicilas

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-03-11-09-39-01.bpo-39829.mlW3Su.rst b/Misc/NEWS.d/next/Core and Builtins/2022-03-11-09-39-01.bpo-39829.mlW3Su.rst
@@ -0,0 +1 @@
+Removed the ``__len__()`` call when initializing a list and moved initializing to ``list_extend``. Patch by Jeremiah Pascual.
diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -865,7 +865,6 @@ list_extend(PyListObject *self, PyObject *iterable)
    PyObject *it;      /* iter(v) */
    Py_ssize_t m;                  /* size of self */
    Py_ssize_t n;                  /* guess for size of iterable */
-    Py_ssize_t mn;                 /* m + n */
    Py_ssize_t i;
    PyObject *(*iternext)(PyObject *);

@@ -889,7 +888,13 @@ list_extend(PyListObject *self, PyObject *iterable)
        /* It should not be possible to allocate a list large enough to cause
        an overflow on any relevant platform */
        assert(m < PY_SSIZE_T_MAX - n);
-        if (list_resize(self, m + n) < 0) {
+        if (self->ob_item == NULL) {
+            if (list_preallocate_exact(self, n) < 0) {
+                return NULL;
+            }
+            Py_SET_SIZE(self, n);
+        }
+        else if (list_resize(self, m + n) < 0) {
            Py_DECREF(iterable);
            return NULL;
        }
@@ -928,10 +933,13 @@ list_extend(PyListObject *self, PyObject *iterable)
         * eventually run out of memory during the loop.
         */
    }
+    else if (self->ob_item == NULL) {
+        if (n && list_preallocate_exact(self, n) < 0)
+            goto error;
+    }
    else {
-        mn = m + n;
        /* Make room. */
-        if (list_resize(self, mn) < 0)
+        if (list_resize(self, m + n) < 0)
            goto error;
        /* Make the list sane again. */
        Py_SET_SIZE(self, m);
@@ -2814,19 +2822,6 @@ list___init___impl(PyListObject *self, PyObject *iterable)
        (void)_list_clear(self);
    }
    if (iterable != NULL) {
-        if (_PyObject_HasLen(iterable)) {
-            Py_ssize_t iter_len = PyObject_Size(iterable);
-            if (iter_len == -1) {
-                if (!PyErr_ExceptionMatches(PyExc_TypeError)) {
-                    return -1;
-                }
-                PyErr_Clear();
-            }
-            if (iter_len > 0 && self->ob_item == NULL
-                && list_preallocate_exact(self, iter_len)) {
-                return -1;
-            }
-        }
        PyObject *rv = list_extend(self, iterable);
        if (rv == NULL)
            return -1;
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Removed the ``__len__()`` call when initializing a list and moved initializing to ``list_extend``. Patch by Jeremiah Pascual.