From 8be26339cba5f933dd63549687a5e5e0560d0e40 Mon Sep 17 00:00:00 2001
From: Bhuvansh Kataria <bhuvanshkataria@gmail.com>
Date: Tue, 28 Jul 2026 12:45:55 +0000
Subject: [PATCH] gh-154817: Fix OrderedDict.pop() crash with inconsistent
 equality

---
 Lib/test/test_ordered_dict.py                 | 22 +++++++++++++++++++
 ...-07-28-17-56-37.gh-issue-154817.PYfwpm.rst |  4 ++++
 Objects/odictobject.c                         |  7 +++++-
 3 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-07-28-17-56-37.gh-issue-154817.PYfwpm.rst

diff --git a/Lib/test/test_ordered_dict.py b/Lib/test/test_ordered_dict.py
index ac24110cf63e823..ba6673cc9cbbb15 100644
--- a/Lib/test/test_ordered_dict.py
+++ b/Lib/test/test_ordered_dict.py
@@ -1014,6 +1014,28 @@ def test_weakref_list_is_not_traversed(self):
 
         gc.collect()
 
+    def test_pop_inconsistent_eq(self):
+        class K:
+            def __init__(self):
+                self.calls = 0
+
+            def __hash__(self):
+                return 12345
+
+            # Behave inconsistently across repeated equality checks.
+            def __eq__(self, other):
+                self.calls += 1
+                return self.calls <= 2
+
+        k1 = K()
+        k2 = K()
+
+        od = self.OrderedDict()
+        od[k1] = "value"
+
+        with self.assertRaises(KeyError):
+            od.pop(k2)
+
 
 class PurePythonOrderedDictSubclassTests(PurePythonOrderedDictTests):
 
diff --git a/Misc/NEWS.d/next/Library/2026-07-28-17-56-37.gh-issue-154817.PYfwpm.rst b/Misc/NEWS.d/next/Library/2026-07-28-17-56-37.gh-issue-154817.PYfwpm.rst
new file mode 100644
index 000000000000000..4e8f3bf2053eff8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-07-28-17-56-37.gh-issue-154817.PYfwpm.rst
@@ -0,0 +1,4 @@
+Fix a crash in collections.OrderedDict.pop() when a key's __eq__
+implementation returns inconsistent results across repeated comparisons.
+OrderedDict.pop() now raises KeyError instead of crashing when no default
+value is provided.
diff --git a/Objects/odictobject.c b/Objects/odictobject.c
index c51fd4b7195da42..9c78808887e0248 100644
--- a/Objects/odictobject.c
+++ b/Objects/odictobject.c
@@ -1095,7 +1095,12 @@ _odict_popkey_hash(PyObject *od, PyObject *key, PyObject *failobj,
         /* Now delete the value from the dict. */
         if (_PyDict_Pop_KnownHash((PyDictObject *)od, key, hash,
                                   &value) == 0) {
-            value = Py_NewRef(failobj);
+            if (failobj) {
+                value = Py_NewRef(failobj);
+            }
+            else {
+                PyErr_SetObject(PyExc_KeyError, key);
+            }
         }
     }
     else if (value == NULL && !PyErr_Occurred()) {