From dc56f5f48866bf3c5412642bba00890d9a090cfb Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Sun, 9 Feb 2020 00:39:28 -0800
Subject: [PATCH] bpo-39590: make deque.__contains__ and deque.count hold
 strong references (GH-18421) (GH-18423)

(cherry picked from commit c6dedde160a9fce5d049e860f586ad8f93aec822)

Co-authored-by: sweeneyde <36520290+sweeneyde@users.noreply.github.com>

Co-authored-by: sweeneyde <36520290+sweeneyde@users.noreply.github.com>
---
 Lib/test/test_deque.py                               | 12 ++++++++++++
 .../Library/2020-02-09-05-51-05.bpo-39590.rf98GU.rst |  1 +
 Modules/_collectionsmodule.c                         |  4 ++++
 3 files changed, 17 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-02-09-05-51-05.bpo-39590.rf98GU.rst

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index 51b66b76aca..c0f7138254f 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -183,6 +183,18 @@ class TestBasic(unittest.TestCase):
         with self.assertRaises(RuntimeError):
             n in d
 
+    def test_contains_count_stop_crashes(self):
+        class A:
+            def __eq__(self, other):
+                d.clear()
+                return NotImplemented
+        d = deque([A(), A()])
+        with self.assertRaises(RuntimeError):
+            _ = 3 in d
+        d = deque([A(), A()])
+        with self.assertRaises(RuntimeError):
+            _ = d.count(3)
+
     def test_extend(self):
         d = deque('a')
         self.assertRaises(TypeError, d.extend, 1)
diff --git a/Misc/NEWS.d/next/Library/2020-02-09-05-51-05.bpo-39590.rf98GU.rst b/Misc/NEWS.d/next/Library/2020-02-09-05-51-05.bpo-39590.rf98GU.rst
new file mode 100644
index 00000000000..68625028fb7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-02-09-05-51-05.bpo-39590.rf98GU.rst
@@ -0,0 +1 @@
+Collections.deque now holds strong references during deque.__contains__ and deque.count, fixing crashes.
\ No newline at end of file
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 45169ecd11a..cc2b90eaa28 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -966,7 +966,9 @@ deque_count(dequeobject *deque, PyObject *v)
     while (--n >= 0) {
         CHECK_NOT_END(b);
         item = b->data[index];
+        Py_INCREF(item);
         cmp = PyObject_RichCompareBool(item, v, Py_EQ);
+        Py_DECREF(item);
         if (cmp < 0)
             return NULL;
         count += cmp;
@@ -1003,7 +1005,9 @@ deque_contains(dequeobject *deque, PyObject *v)
     while (--n >= 0) {
         CHECK_NOT_END(b);
         item = b->data[index];
+        Py_INCREF(item);
         cmp = PyObject_RichCompareBool(item, v, Py_EQ);
+        Py_DECREF(item);
         if (cmp) {
             return cmp;
         }