https://github.com/python/cpython/commit/5539c2a5437acc4f4719aabac375368e0d310bd9 commit: 5539c2a5437acc4f4719aabac375368e0d310bd9 branch: main author: tonghuaroot (童话) <[email protected]> committer: eendebakpt <[email protected]> date: 2026-09-17T21:11:17+02:00 summary:
gh-154594: Fix deepcopy memo lookup when __deepcopy__ returns None (#154595) * gh-154594: Fix deepcopy memo lookup when __deepcopy__ returns None * Use 'd in memo' lookup instead of a sentinel Addresses review: clearer, no sentinel, and the test treats memo as opaque. * Apply review suggestions: shorten NEWS, use class attribute in test --------- Co-authored-by: Pieter Eendebak <[email protected]> files: A Misc/NEWS.d/next/Library/2026-07-24-00-02-00.gh-issue-154594.Xk7mQ2.rst M Lib/copy.py M Lib/test/test_copy.py diff --git a/Lib/copy.py b/Lib/copy.py index 6149301ad1389e..f7fd680657b85a 100644 --- a/Lib/copy.py +++ b/Lib/copy.py @@ -122,9 +122,8 @@ def deepcopy(x, memo=None): if memo is None: memo = {} else: - y = memo.get(d, None) - if y is not None: - return y + if d in memo: + return memo[d] copier = _deepcopy_dispatch.get(cls) if copier is not None: diff --git a/Lib/test/test_copy.py b/Lib/test/test_copy.py index 13b7ce29565dee..2a12a6737df163 100644 --- a/Lib/test/test_copy.py +++ b/Lib/test/test_copy.py @@ -951,6 +951,17 @@ def m(self): self.assertIs(g.b.__self__, g) g.b() + def test_deepcopy_memo_none_result(self): + # Objects whose deepcopy result is None must still be memoized. + class C: + call_count = 0 + def __deepcopy__(self, memo): + C.call_count += 1 + return None + obj = C() + copy.deepcopy([obj, obj, obj]) + self.assertEqual(C.call_count, 1) + class TestReplace(unittest.TestCase): diff --git a/Misc/NEWS.d/next/Library/2026-07-24-00-02-00.gh-issue-154594.Xk7mQ2.rst b/Misc/NEWS.d/next/Library/2026-07-24-00-02-00.gh-issue-154594.Xk7mQ2.rst new file mode 100644 index 00000000000000..5f96bba97aa19f --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-07-24-00-02-00.gh-issue-154594.Xk7mQ2.rst @@ -0,0 +1,2 @@ +Fix :func:`copy.deepcopy` so that an object whose deep copy is ``None`` is +still memoized. Patch by tonghuaroot. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
