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GeezerVison is showing github.com — gh-131510: Deprecate PyUnicodeObject structs, revert memory layout by encukou · Pull Request #130697 · python/cpython

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@encukou

@encukou encukou commented Feb 28, 2025 •
edited by bedevere-app Bot
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(Draft for discussion with the C API WG.)

Deprecate PyASCIIObject, PyCompactUnicodeObject, PyUnicodeObject structs, and the PyUnicode_IS_COMPACT macro.

Schedule removal for 3.16, the shortest non-exceptional deprecation period per PEP-387. The structs are blocking development of the free-threaded build (bitfields can't be used atomically) and of possible UTF-8-focused string representations.
Add an example of what I'd like to see in porting notes for a deprecation.

In non-free-threaded builds, revert PyASCIIObject to be ABI-compatible with in 3.13.

For free-threaded builds, use alignas instead of padding to ensure alignment.
All relevant compilers support alignas, as do the C11 & C++11 standards, but they may need different spelling or compiler options for it.
Introduce _Py_ALIGN_AS for this.

📚 Documentation preview 📚: https://cpython-previews--130697.org.readthedocs.build/

  • Issue: Deprecate PyASCIIObject/PyUnicodeObject #131510

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encukou added 2 commits February 28, 2025 18:03
@encukou
Deprecate PyUnicodeObject structs, revert memory layout
6d266ee 
Deprecate `PyASCIIObject`, `PyCompactUnicodeObject`, `PyUnicodeObject`
structs, and the `PyUnicode_IS_COMPACT` macro.

Schedule removal for 3.16, the shortest non-exceptional
deprecation period per PEP-387. The structs are blocking development
of the free-threaded build (bitfields can't be used atomically)
and of possible UTF-8-focused string representations.

In non-free-threaded builds, revert `PyASCIIObject` to the binary
layout used in 3.13.

For free-threaded builds, use `alignas` instead of padding to ensure
alignment.
All relevant compilers support `alignas`, as do the C11 & C++11 standards,
but they may need different spelling or compiler options for it.
@encukou
Fix footnote numbers
2611679
@encukou

encukou commented Feb 28, 2025

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Discussion: https://discuss.python.org/t/deprecating-the-pyasciiobject-struct/82543

I'll look at the compile errors later. (Thank you GHA; I can't easily do a matrix build locally.)
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encukou added 6 commits March 3, 2025 17:41
@encukou
Add function for 'interned' writes; fix type for free-threaded builds…
2451a86 
… (unit8)
@encukou
Define _Py_ALIGN_AS for GCC on C++03 and below
351f0e3
@encukou
Fix generators & run regen
f0fc819
@encukou
Use __declspec(align) on MSVC
19ed310
@encukou
Regen test_frozenmain
bf4086c
@encukou
Merge in the main branch
500b483
@encukou encukou added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Mar 5, 2025
@bedevere-bot

bedevere-bot commented Mar 5, 2025

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🤖 New build scheduled with the buildbot fleet by @encukou for commit 500b483 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F130697%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.
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@bedevere-bot bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Mar 5, 2025
encukou added 2 commits March 20, 2025 14:34
@encukou
Merge in the main branch
849384e
@encukou
Use __attribute__ for GCC & clang pre-C11 pedantic mode
e247c74
@encukou encukou added skip news and removed skip news labels Mar 20, 2025
encukou added 3 commits March 20, 2025 15:12
@encukou
Make the structs PyUnstable
d10dcdc
@encukou
Add docs for unstable API
86d41ea
@encukou
Test PyUnstable_Unicode_GET_CACHED_HASH
87a5d30
@encukou encukou changed the title Deprecate PyUnicodeObject structs, revert memory layout gh-131510: Deprecate PyUnicodeObject structs, revert memory layout Mar 20, 2025
@bedevere-app bedevere-app Bot mentioned this pull request Mar 20, 2025
Deprecate PyASCIIObject/PyUnicodeObject #131510
Closed
encukou added 4 commits March 20, 2025 16:12
@encukou
What's New for the additions
d5939cf
@encukou
versionadded, rewording
3c861bc
@encukou
blurb
6f23304
@encukou
regen
5dbd6db
@encukou encukou mentioned this pull request Mar 20, 2025
Deprecate & plan to remove PyASCIIObject & co. capi-workgroup/decisions#60
Closed
2 of 6 tasks
serhiy-storchaka
serhiy-storchaka reviewed Apr 7, 2025
View reviewed changes
Comment thread Include/pymacro.h
&& (defined(__GNUC__) || defined(__clang__))
# define _Py_ALIGN_AS(V) __attribute__((aligned(V)))
# else
# define _Py_ALIGN_AS(V) alignas(V)

@serhiy-storchaka serhiy-storchaka Apr 7, 2025

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This will be used if __cplusplus < 201103L and neither __GNUC__ nor __clang__ are defined.

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@encukou encukou Apr 28, 2025

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That's unknown compilers that aren't in C++11+-standard mode.
IMO, the best we can do is hope that they do support this part of C++11.

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@serhiy-storchaka serhiy-storchaka Apr 28, 2025

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What if it is an old Microsoft compiler? Then we could use __declspec(align(V)).

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@encukou

encukou commented Apr 28, 2025

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It's not yet time to deprecate these. I'll send a new PR for the memory layout revert.
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@encukou encukou closed this Apr 28, 2025
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@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently will be requested when the pull request is marked ready for review ericsnowcurrently is a code owner
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@encukou @bedevere-bot @serhiy-storchaka
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