PEP 7: Python 3.11 uses C99 and C11 by vstinner · Pull Request #2309 · python/peps · GitHub

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Update PEP 7 to reflect what's being used in practice: https://docs.python.org/dev/whatsnew/3.11.html#build-changes

Building Python now requires a C99 <math.h> header file providing the following functions: copysign(), hypot(), isfinite(), isinf(), isnan(), round(). (Contributed by Victor Stinner in bpo-45440.)
Building Python now requires a C99 <math.h> header file providing a NAN constant, or the __builtin_nan() built-in function. If a platform does not support Not-a-Number (NaN), the Py_NO_NAN macro can be defined in the pyconfig.h file. (Contributed by Victor Stinner in bpo-46640.)

IMO it's no longer worth it to go into details of which C99 features are used or not.

See https://bugs.python.org/issue46640 for @encukou's request about updating the PEP.

I'm only aware of one C99 feature which is causing troubles: https://bugs.python.org/issue40120 This issue is still being discussed, I prefer to not mention it in the PEP.

Two on grammar

A

We cannot require full C11 compatibility becase we have to special case MSVC. MSVC does not implement C11 features. Instead MSVC provides substitutes for APIs. For example MSVC has interlocked variable access instead of stdatomic.

C11 stdatomic.h https://en.cppreference.com/w/c/atomic
MSVC Interlocked Variable Access https://docs.microsoft.com/de-de/windows/win32/sync/interlocked-variable-access

GCC < 4.8 and AFAIK clang < 4.0 are lacking stdatomic support. I'm unsure about ICC. I found second hand information that ICC < 18 has incomplete stdatomic.h. I asked somebody to look into AIX xlc.

We cannot require full C11 compatibility

My change doesn't require C11, but C99.

Two on grammar

Fixed.

cc @gpshead @encukou @pablogsal: Is it ok to require C99 to build Python 3.11? I don't think that we have to go into the details of which C99 features are used by Python, do you?

Where was the discussion leading to this PEP change? It shouldn't be happening on this PR -- the peps repo is not for discussions about contents.

@gvanrossum:

Where was the discussion leading to this PEP change? It shouldn't be happening on this PR -- the peps repo is not for discussions about contents.

https://bugs.python.org/issue46640#msg412728

That discussion is far from conclusive. Please escalate to python-dev.

That discussion is far from conclusive. Please escalate to python-dev.

Oh, I didn't expect this change to be controversial. Anyway, I created a thread on python-dev: https://mail.python.org/archives/list/python-dev@python.org/thread/J5FSP6J4EITPY5C2UJI7HSL2GQCTCUWN/

The current version LGTM from a PEP editor perspective, though you may need to modify it pending the outcome of the Python-Dev discussion (C11? Mention C99 features dropped in C11? Explicitly call out features unsupported in MSVC? Clarify that optional features are not supported? Add optional atomic support? etc)

I created a thread on python-dev: https://mail.python.org/archives/list/python-dev@python.org/thread/J5FSP6J4EITPY5C2UJI7HSL2GQCTCUWN/

There is a consensus on using C99 and a willingness to even use some C11 feature, so I updated my PR for that.

@tiran @mdickinson: Does it look good to you?

The public C API should be compatible with C11 as well.
C11 made several features present in C99 optional (most notably variable-length arrays, MSVC doesn't have). Those shouldn't be used in the API.

Ok, let me try something simpler: "Python 3.11 and newer versions use C11 without optional features". Is it better? (see the updated PR)

Not sure if you want to add a reference for that, but a simple overview is:
https://en.wikipedia.org/wiki/C11_%28C_standard_revision%29#Optional_features

That indeed seems helpful

One grammar correction; otherwise LGTM from a textual perspective. Adding a link to C11 seems to be a good idea, though.

Suggested change

      
            * Python 3.6 to 3.10 uses C89 with several select C99 features:
          
            * Python 3.6 to 3.10 use C89 with several select C99 features:

Plural agreement error (grammar)

Once CAM approves this can go in. Thanks for pushing for this!

The latest version of the PR says "C11 without optional features" -- ideally the PR title should be updated before merging too for an accurate commit message.

A

The latest version of the PR says "C11 without optional features" -- ideally the PR title should be updated before merging too for an accurate commit message.

I changed the commit title. GitHub keeps the original commit title. When I click on merge, it uses the commit title, but not the GitHub PR title... I hate that part of GitHub. Gerrit is way better for that, it's possible to review the commit message.

Merged, thanks for the reviews.

The latest version of the PR says "C11 without optional features" -- ideally the PR title should be updated before merging too for an accurate commit message.

I changed the commit title. GitHub keeps the original commit title. When I click on merge, it uses the commit title, but not the GitHub PR title... I hate that part of GitHub. Gerrit is way better for that, it's possible to review the commit message.

Must be your git(hub) tooling. When I merge (in the browser) I get to edit the commit title and message.

Must be your git(hub) tooling. When I merge (in the browser) I get to edit the commit title and message.

Yes. I also get a form to edit the PR title. But in my experience, if I modify the commit title in Git and then use git push --force, the GitHub PR title is not updated. And when I merge a PR, the edit form gives me the title from Git as expected.

It's just that I'm too lazy sometimes to update them :-)

Anyway, I modified the merged commit title to omit C99 :-)

Yeah, the PR title is auto-filled from the initial commit message if the PR branch only has one commit, but otherwise independent of the commit message, since PRs can have any number of commits and it wouldn't really make sense to arbitrarily lock it to one of them. The PR title can be changed at any time, and the commit message can likewise be modified at will when merging.

Anyway, I modified the merged commit title to omit C99 :-)

On main? 😱

On main? scream

I used the merge form to clean up the commit message. See the final commit: e846b70

Understood, thanks. I apologize for the confusion; my fault there.

vstinner requested review from gvanrossum and warsaw as code owners February 7, 2022 14:18

the-knights-who-say-ni added the CLA signed label Feb 7, 2022

AA-Turner reviewed Feb 7, 2022

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Comment thread pep-0007.txt Outdated

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CAM-Gerlach reviewed Feb 15, 2022

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CAM-Gerlach changed the title Python 3.11 uses C99 PEP 7: Require C99 for Python 3.11+ Feb 16, 2022

vstinner changed the title PEP 7: Require C99 for Python 3.11+ PEP 7: Python 3.11 uses C99 and C11 Feb 23, 2022

vstinner mentioned this pull request Feb 23, 2022

bpo-46656: Remove Py_NO_NAN macro python/cpython#31160

Merged

encukou reviewed Feb 24, 2022

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PEP 7: Python 3.11 uses C11

b230af8

CAM-Gerlach reviewed Feb 24, 2022

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gvanrossum reviewed Feb 24, 2022

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Comment thread pep-0007.txt Outdated

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vstinner added 2 commits February 25, 2022 00:06

Grammar; remove Future C99 features

cd43ebe

Add link

2864440

vstinner merged commit e846b70 into python:main Feb 24, 2022

vstinner deleted the pep7 branch February 24, 2022 23:13

erlend-aasland mentioned this pull request May 13, 2022

pep8/greppable exception messages erlend-aasland/peps#1

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erlend-aasland mentioned this pull request Jun 27, 2022

pep 687/mark as accepted erlend-aasland/peps#2

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+              * Python 3.11 and newer versions use C99 in the public C API and use a
+                subset of C11 in Python internals. The public C API should be
+                compatible with C++. The C11 subset are features supported by GCC 8.5,
+                clang 8.0, and MSVC of Visual Studio 2017.

	* Python 3.6 to 3.10 uses C89 with several select C99 features:
	* Python 3.6 to 3.10 use C89 with several select C99 features:

PEP 7: Python 3.11 uses C99 and C11 by vstinner · Pull Request #2309 · python/peps · GitHub

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PEP 7: Python 3.11 uses C99 and C11 - #2309

PEP 7: Python 3.11 uses C99 and C11#2309vstinner merged 3 commits intopython:mainpython/peps:mainfrom vstinner:pep7Copy head branch name to clipboard

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PEP 7: Python 3.11 uses C99 and C11#2309
vstinner merged 3 commits into
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