bpo-39829: __len__() called twice when constructing a list

thatbirdguythatuknownot · web-flow · commit 75ec222c2ec8 · 2022-03-10T08:34:30.000+08:00
diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -933,7 +933,7 @@ list_extend(PyListObject *self, PyObject *iterable)
          * eventually run out of memory during the loop.
          */
     }
-    else if (self->ob_item == NULL) {
+    else if (n && self->ob_item == NULL) {
         if (list_preallocate_exact(self, n) < 0)
             goto error;
     }

Original file line number	Diff line number	Diff line change
`@@ -933,7 +933,7 @@ list_extend(PyListObject self, PyObject iterable)`
`933`	`933`	`* eventually run out of memory during the loop.`
`934`	`934`	`*/`
`935`	`935`	`}`
`936`		`- else if (self->ob_item == NULL) {`
	`936`	`+ else if (n && self->ob_item == NULL) {`
`937`	`937`	`if (list_preallocate_exact(self, n) < 0)`
`938`	`938`	`goto error;`
`939`	`939`	`}`