gh-85943: Fix BytesWarning in the struct format cache under -bb#153627
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serhiy-storchaka merged 1 commit intoJul 17, 2026
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Normalize bytes format strings to str before using them as the cache key, so that equal str and bytes formats no longer collide and get compared. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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needs backport to 3.13
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Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15. |
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GH-153834 is a backport of this pull request to the 3.15 branch. |
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Sorry, @serhiy-storchaka, I could not cleanly backport this to |
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GH-153835 is a backport of this pull request to the 3.14 branch. |
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GH-153836 is a backport of this pull request to the 3.13 branch. |
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GH-153627) (GH-153835) Normalize bytes format strings to str before using them as the cache key, so that equal str and bytes formats no longer collide and get compared. (cherry picked from commit 190d2ff) Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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GH-153627) (GH-153834) Normalize bytes format strings to str before using them as the cache key, so that equal str and bytes formats no longer collide and get compared. (cherry picked from commit 190d2ff) Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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The
structmodule caches compiledStructobjects in a dict keyed by theformat string. Since an ASCII
strand the equalbytesobject have the samehash, using a
strformat after an equalbytesformat (or vice versa) makesthe dict compare keys of different types, which raises
BytesWarningunder the-bbcommand line option:Fix it by decoding a
bytesformat tostr(the same wayStruct()alreadydoes) before using it as the cache key, so equal
strandbytesformats mapto a single entry and are never compared to each other.
python -bb,struct.calcsizeraises a warning when used with str argument after being used with bytes (might be a larger problem with dicts) #85943