[3.8] bpo-39453: Fix contains method of list to hold strong references (GH-18204)
diff --git a/Lib/test/test_list.py b/Lib/test/test_list.py
index f4dcced..105ef65 100644
--- a/Lib/test/test_list.py
+++ b/Lib/test/test_list.py
@@ -216,6 +216,13 @@
with self.assertRaises(ValueError):
lst.remove(lst)
+ # bpo-39453: list.__contains__ was not holding strong references
+ # to list elements while calling PyObject_RichCompareBool().
+ lst = [X(), X()]
+ 3 in lst
+ lst = [X(), X()]
+ X() in lst
+
if __name__ == "__main__":
unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-01-25-23-51-17.bpo-39453.xCOkYk.rst b/Misc/NEWS.d/next/Core and Builtins/2020-01-25-23-51-17.bpo-39453.xCOkYk.rst
new file mode 100644
index 0000000..8c2e49f
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-01-25-23-51-17.bpo-39453.xCOkYk.rst
@@ -0,0 +1,2 @@
+Fixed a possible crash in :meth:`list.__contains__` when a list is changed
+during comparing items. Patch by Dong-hee Na.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 73afc44..3044408 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -445,12 +445,16 @@
static int
list_contains(PyListObject *a, PyObject *el)
{
+ PyObject *item;
Py_ssize_t i;
int cmp;
- for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i)
- cmp = PyObject_RichCompareBool(el, PyList_GET_ITEM(a, i),
- Py_EQ);
+ for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i) {
+ item = PyList_GET_ITEM(a, i);
+ Py_INCREF(item);
+ cmp = PyObject_RichCompareBool(el, item, Py_EQ);
+ Py_DECREF(item);
+ }
return cmp;
}