OrderedDict.pop() can segfault when key equality changes between lookups

[BHUVANSH855]

Crash report

What happened?

Calling collections.OrderedDict.pop() without a default value can cause a segmentation fault if the lookup key has a stateful __eq__ implementation that returns different results across successive comparisons.

The crash occurs on the current main branch.

Minimal reproducer:

from collections import OrderedDict

class K:
    def __init__(self):
        self.calls = 0

    def __hash__(self):
        return 12345

    def __eq__(self, other):
        self.calls += 1
        return self.calls == 1

k1 = K()
k2 = K()

od = OrderedDict()
od[k1] = "value"

od.pop(k2)

Running this with a locally built CPython from main results in:

Segmentation fault (core dumped)

Expected behavior:

• OrderedDict.pop() should not crash the interpreter.
• It should either remove the matching item or raise KeyError if the key is not found.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.16.0a0 (heads/fix-odict-pop-null-failobj:2ffab083782, Jul 28 2026, 12:31:11) [GCC 13.3.0]

Linked PRs

• gh-154817: Fix OrderedDict.pop() crash with inconsistent equality #154818

[picnixz]

I believe there is already an issue about this, whether specific or general avout OrderedDict. Please check

[BHUVANSH855]

I believe there is already an issue about this, whether specific or general avout OrderedDict. Please check

I searched for existing issues related to OrderedDict.pop() crashes and OrderedDict/__eq__ interactions.

I found issues such as #142637 (re-entrant __eq__) and #142734 (re-entrant __getitem__), but they appear to be different issues. This crash does not require re-entrancy or mutation during comparison; it can be reproduced with a stateful __eq__ implementation that simply returns different results across successive comparisons.

If there is another issue that matches this case more closely, I'd be happy to retarget this or close it as a duplicate.