From 0f3e1024819b69c9adbefb03ec8e5f6205a5e75b Mon Sep 17 00:00:00 2001
From: sweeneyde <sweeney.427@osu.edu>
Date: Fri, 23 Jul 2021 21:59:57 -0400
Subject: [PATCH 1/3] Don't crash when calling
 weakref.proxy(not_an_iterator).__next__

---
 Lib/test/test_weakref.py | 30 ++++++++++++++++++++++++++++++
 Objects/weakrefobject.c  |  6 ++++++
 2 files changed, 36 insertions(+)

diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
index dd5a781ed59d8b..acd7284c0d7f09 100644
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -411,6 +411,36 @@ def __iter__(self):
             # can be killed in the middle of the call
             "blech" in p
 
+    def test_proxy_next(self):
+        arr = [4, 5, 6]
+        def iterator_func():
+            yield from arr
+        it = iterator_func()
+
+        class IteratesWeakly:
+            def __iter__(self):
+                return weakref.proxy(it)
+
+        weak_it = IteratesWeakly()
+
+        # Calls proxy.__next__
+        self.assertEqual(list(weak_it), [4, 5, 6])
+
+    def test_proxy_bad_next(self):
+        # bpo-44720: PyIter_Next() shouldn't be called if the reference
+        # isn't an iterator.
+
+        not_an_iterator = lambda: 0
+
+        class A:
+            def __iter__(self):
+                return weakref.proxy(not_an_iterator)
+        a = A()
+
+        msg = "Weakref referenced a non-iterator"
+        with self.assertRaisesRegex(TypeError, msg):
+            list(a)
+
     def test_proxy_reversed(self):
         class MyObj:
             def __len__(self):
diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index c36d2395cc8c53..733aa5b57a8bc8 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -657,6 +657,12 @@ proxy_iternext(PyWeakReference *proxy)
         return NULL;
 
     PyObject *obj = PyWeakref_GET_OBJECT(proxy);
+    if (!PyIter_Check(obj)) {
+        PyErr_Format(PyExc_TypeError,
+                     "Weakref referenced a non-iterator '%.200s' object",
+                     Py_TYPE(obj)->tp_name);
+        return NULL;
+    }
     Py_INCREF(obj);
     PyObject* res = PyIter_Next(obj);
     Py_DECREF(obj);

From 5af7c2c4b3dabd2162ac2b970017213af3e54591 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Sat, 24 Jul 2021 02:18:00 +0000
Subject: [PATCH 2/3] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../NEWS.d/next/Library/2021-07-24-02-17-59.bpo-44720.shU5Qm.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2021-07-24-02-17-59.bpo-44720.shU5Qm.rst

diff --git a/Misc/NEWS.d/next/Library/2021-07-24-02-17-59.bpo-44720.shU5Qm.rst b/Misc/NEWS.d/next/Library/2021-07-24-02-17-59.bpo-44720.shU5Qm.rst
new file mode 100644
index 00000000000000..83694f3988ae9a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-07-24-02-17-59.bpo-44720.shU5Qm.rst
@@ -0,0 +1 @@
+``weakref.proxy`` objects referencing non-iterators now raise ``TypeError`` rather than dereferencing the null ``tp_iternext`` slot and crashing.
\ No newline at end of file

From 7847f1a5293638d61262ad994a9fcb12c476e460 Mon Sep 17 00:00:00 2001
From: sweeneyde <sweeney.427@osu.edu>
Date: Fri, 23 Jul 2021 22:24:56 -0400
Subject: [PATCH 3/3] Error message: Weakref --> Weakref proxy

---
 Lib/test/test_weakref.py | 2 +-
 Objects/weakrefobject.c  | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
index acd7284c0d7f09..1a5314ccff315a 100644
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -437,7 +437,7 @@ def __iter__(self):
                 return weakref.proxy(not_an_iterator)
         a = A()
 
-        msg = "Weakref referenced a non-iterator"
+        msg = "Weakref proxy referenced a non-iterator"
         with self.assertRaisesRegex(TypeError, msg):
             list(a)
 
diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index 733aa5b57a8bc8..bb56c7dbdb8322 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -659,8 +659,8 @@ proxy_iternext(PyWeakReference *proxy)
     PyObject *obj = PyWeakref_GET_OBJECT(proxy);
     if (!PyIter_Check(obj)) {
         PyErr_Format(PyExc_TypeError,
-                     "Weakref referenced a non-iterator '%.200s' object",
-                     Py_TYPE(obj)->tp_name);
+            "Weakref proxy referenced a non-iterator '%.200s' object",
+            Py_TYPE(obj)->tp_name);
         return NULL;
     }
     Py_INCREF(obj);