gh-154594: Fix deepcopy memo lookup when __deepcopy__ returns None#154595
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tonghuaroot wants to merge 1 commit into
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gh-154594: Fix deepcopy memo lookup when __deepcopy__ returns None#154595tonghuaroot wants to merge 1 commit into
tonghuaroot wants to merge 1 commit into
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PR #138429 (gh-132657) replaced the memo-miss sentinel from
_nil = []toNonefor free-threading performance. ButNoneis a valid deepcopy result, somemo.get(d, None)can't distinguish "not found" from "found None". This skips memoization for None-valued results, causing redundant__deepcopy__calls.Fix: use a private
_MEMO_MISS = object()sentinel. Immortalized objects have no refcount contention, so the FT benefit is preserved.