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

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-154818

Beginne mit dem OrderedDict.pop()-Einstiegspunkt und führe den minimalen Reproducer auf einem lokal gebauten CPython-main-Branch aus. Als abgeschlossen gilt die Aufgabe, wenn der Reproducer nicht mehr mit einem Segmentation Fault abstürzt und pop() entweder das passende Element entfernt oder KeyError auslöst, wenn kein Schlüssel gefunden wird.