LDLIBRARY is set to libpython3.9a although no static lib is included in mambaforge for Linux

[maxnoe]

Solution to issue cannot be found in the documentation.

• I checked the documentation.

Issue

Compiling software, I use sysconfig.get_config_var("LDLIBRARY") to get the name of the python library.

In a fresh mambaforge installation, this variable is set to libpython3.9.a but only shared libraries are present in the lib dir:

❯ python -c 'import sysconfig; print(sysconfig.get_config_var("LDLIBRARY"))'
libpython3.9.a

❯ ls -1 ~/.local/conda/lib/libpython*
/home/mnoethe/.local/conda/lib/libpython3.9.so
/home/mnoethe/.local/conda/lib/libpython3.9.so.1.0
/home/mnoethe/.local/conda/lib/libpython3.so

Installed packages

Fresh mambaforge installation

Environment info

❯ conda info

     active environment : base
    active env location : /home/mnoethe/.local/conda
            shell level : 1
       user config file : /home/mnoethe/.condarc
 populated config files : /home/mnoethe/.local/conda/.condarc
          conda version : 4.11.0
    conda-build version : not installed
         python version : 3.9.7.final.0
       virtual packages : __linux=5.14.0=0
                          __glibc=2.31=0
                          __unix=0=0
                          __archspec=1=x86_64
       base environment : /home/mnoethe/.local/conda  (writable)
      conda av data dir : /home/mnoethe/.local/conda/etc/conda
  conda av metadata url : None
           channel URLs : https://conda.anaconda.org/conda-forge/linux-64
                          https://conda.anaconda.org/conda-forge/noarch
          package cache : /home/mnoethe/.local/conda/pkgs
                          /home/mnoethe/.conda/pkgs
       envs directories : /home/mnoethe/.local/conda/envs
                          /home/mnoethe/.conda/envs
               platform : linux-64
             user-agent : conda/4.11.0 requests/2.26.0 CPython/3.9.7 Linux/5.14.0-1027-oem ubuntu/20.04.4 glibc/2.31
                UID:GID : 5074:5002
             netrc file : None
           offline mode : False

[isuruf]

You need to install libpython-static package.

[maxnoe]

@isuruf I don't want to have the static lib. This is about that the python package has the wrong sysconfig variable in the metadata.

sysconfig.get_config_var("LDLIBRARY") should point to an existing file, in this case the libpython3.9.so

[hmaarrfk]

For what its worth, it also affects 3.10.

We might to patch something here
https://github.com/python/cpython/blob/39a54ba63850e081a4a5551a773df5b4d5b1d3cd/Lib/sysconfig.py#L628

[hmaarrfk]

I'm not sure if this is something that we can work with upstream on.

I'm not really sure what the correct behavior is:

1. Return .so when -static isn't installed.
2. Return .a when -static is installed

Do we want the above?

[mgorny]

I'm not really sure what the correct behavior is:

1. Return `.so` when `-static` isn't installed.

2. Return `.a` when `-static` is installed

Do we want the above?

I don't think so. I mean, you don't want packages to be switching between shared and static libpython based on whether libpython-static happens to be installed or not.

Pretty much all distros (checked Arch, Debian, Gentoo and openSUSE right now) have LDLIBRARY pointing to .so. I think this is a reasonable default, given that 1) you generally want to prefer dynamic linking, and 2) it is always installed.

FWICS Python defaults to using the shared library in _sysconfigdata_* if --enable-shared is passed. What I don't really know is whether there's a specific reason we're installing the data from the static build rather than the shared build. I'm building the packages locally to check the diff now.

[mgorny]

Looks like most of the differences are superficial (build paths, build-time details), but some of the differences suggest that we're probably wrong to be using this data:

-    'CFLAGSFORSHARED': '',
+    'CFLAGSFORSHARED': '-fPIC',
-    'INSTSONAME': 'libpython3.14.a',
+    'INSTSONAME': 'libpython3.14.so.1.0',
-    'Py_ENABLE_SHARED': 0,
+    'Py_ENABLE_SHARED': 1,