gh-82909: Update PC/pyconfig.h to allow disabling pragma based auto-linking #19740

jcfr · 2020-04-27T19:19:02Z

Define PY_NO_LINK_LIB to build extension disabling pragma based
auto-linking. This is relevant when using build-system generator
(e.g CMake) where the linking is explicitly handled

https://bugs.python.org/issue38728

Issue: Update PC/pyconfig.h to support disabling auto linking #82909

jcfr · 2020-05-06T20:06:22Z

@zooba Thanks for your patience, let me know if you need anything else to move forward with the integration 🙏

mathstuf · 2020-05-12T23:31:03Z

No news entry in Misc/NEWS.d/next/

@jcfr Seems like a release note could be added in the meantime.

mathstuf · 2020-09-16T12:24:34Z

Ping? Any update here? It'd be nice to have this in 3.9.

mathstuf · 2021-09-05T03:03:39Z

Seems this will miss 3.10 as well.

kwryankrattiger · 2021-12-09T17:23:48Z

Ping. This would be really really nice to have sometime soon 👍

zooba · 2021-12-09T20:25:32Z

I thought we'd already added this? I guess if it's not there, then we should.

Definitely needs a NEWS entry, probably deserves a What's New as well. Not sure if there's any place in the documentation that would suit, but if so, we should mention it for sure.

jcfr · 2021-12-09T21:06:11Z

Definitely needs a NEWS entry

I can definitely add an entry, What about the C-API section ? See https://github.com/python/cpython/tree/main/Misc/NEWS.d/next/C%20API

arhadthedev · 2023-04-02T12:43:44Z

I added draft documentation and the NEWS entry for the macro. However, they need improvements.

jcfr · 2023-04-03T02:38:02Z

@arhadthedev Thanks for your help moving this forward 🙏

zooba · 2023-04-03T15:47:43Z

I haven't tested the commands added to the docs, but if they do work as described and produce the files, then this looks fine to me.

tasty0tomato · 2023-06-26T02:43:13Z

It seems that if building Python by oneself, python's lib file will not be found in virtual environment. Hope this issue fixes as quickly as possible

zooba · 2023-06-26T16:21:24Z

No, virtual environment is only for Python libraries. You'll need to look in base_prefix to find native import libraries.

tasty0tomato · 2023-06-26T22:54:03Z

@zooba My question is like this:rosinality/stylegan2-pytorch#325 (comment)

So, is it more like to be a question about venv?

zooba · 2023-06-27T11:41:30Z

It looks like Torch is deciding those settings, and it's deciding wrong about where to find the libs files.

There's a revamp of sysconfig going on that will eventually provide a better option for them to find it, but for now, either they need to use sys.base_prefix instead of sys.prefix, or if they already are (which they might be), then there's something wrong with your venv (maybe you've chained multiple venvs together in some unsupported way?)

tasty0tomato · 2023-06-27T23:58:57Z

@zooba I can give some additional informations. For exmaple,
The source code of python is on D:\Python-3.10.12,
The binary file of Windows and also the dll file are on D:\Python-3.10.12\PCbuild\amd64

And that's maybe why dll file cannot be found?

zooba · 2023-06-28T15:59:00Z

Yeah, many tools are not going to work well when running from a CPython build directory. It's an unsupported configuration.

Try using the PC/layout tool (e.g. python PC\layout --copy <directory> --preset-default) to create an installed-shape directory. That will have the libs at the usual place relative to python.exe. (You need to re-run the command if you rebuild Python, but it does incremental copying. Also, don't run the copied Python from the CPython source directory or it'll get the wrong Lib dir.)

mathstuf · 2023-12-28T05:37:18Z

Any progress here? I see conflicts, so at least a rebase is in order. It'd be nice to get this into 3.13 at least…

@vstinner Interested in shepherding this C API change at all?

zooba · 2023-12-28T12:16:04Z

A rebase ought to be enough, and when someone confirms that the build commands shown in the new documentation are correct then this can be merged (as per my last message).

KerstinKeller · 2024-11-21T14:28:20Z

This would potentially be extremly helpful, any chance that this will get merged at some point?

zooba · 2024-11-21T14:37:42Z

It looks like the rebase isn't coming, so someone will need to submit a new PR.

It also looks like my last hesitation was that the commands in the docs weren't tested.

Doc/whatsnew/3.12.rst

…linking Define PY_NO_LINK_LIB to build extension disabling pragma based auto-linking. This is relevant when using build-system generator (e.g CMake) where the linking is explicitly handled

zooba

Nothing wrong with the PR as it is, but I think we can do a bit of tidying here if you want.

zooba · 2025-03-03T13:07:24Z

PC/pyconfig.h.in

 #ifdef MS_COREDLL
 #       if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
                /* not building the core - must be an ext */
-#               if defined(_MSC_VER)
+#               if defined(_MSC_VER) && !defined(Py_NO_LINK_LIB)


This whole set of conditions is pretty ugly... any interest in simplifying?

Ideally in this order:

check if the feature is explicitly disabled (new variable)

check if we're in a context where it should be implicitly disabled (Py_BUILD_CORE[_BUILTIN])

check if the compiler supports it (_MSC_VER)

The order doesn't need to be spelled out to anyone reading it, but it should make it easiest to read (the first check has the best name) and easiest to maintain (alternate compilers can be supported in the "middle", not the edges).

It also really doesn't need to be indented by 8 characters. Four would be plenty.

zooba · 2025-03-03T13:08:31Z

PC/pyconfig.h.in

+                        /* Define Py_NO_LINK_LIB to build extension disabling pragma
+                        based auto-linking.
+                        This is relevant when using build-system generator (e.g CMake) where
+                        the linking is explicitly handled */


This comment isn't important for this file, though a short header above the entire block (something like "automatically reference python3x.lib") might make it easier to understand the purpose without reading the whole way through.

zooba · 2025-03-10T17:39:51Z

Guess we're not getting those improvements, so we'll leave them for later. Should be an easy first contribution for a sprint.

jcfr · 2025-03-15T06:48:09Z

Thanks everyone for the help moving this forward 🙏

…auto-linking (pythonGH-19740) Define Py_NO_LINK_LIB to build extension disabling pragma based auto-linking. This is relevant when using build-system generator (e.g CMake) where the linking is explicitly handled

hroncok · 2025-05-29T11:09:33Z

Doc/extending/windows.rst

+   :file:`Python.h` triggers an implicit, configure-aware link with the
+   library.  The header file chooses :file:`pythonXY_d.lib` for Debug,
+   :file:`pythonXY.lib` for Release, and :file:`pythonX.lib` for Release with
+   the `Limited API <stable-application-binary-interface>`_ enabled.


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gh-82909: Update PC/pyconfig.h to allow disabling pragma based auto-linking #19740

gh-82909: Update PC/pyconfig.h to allow disabling pragma based auto-linking #19740

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