Thread

Re: Python Limited API for PL/Python on MSVC

Bryan Green <dbryan.green@gmail.com> — 2025-12-30T15:55:24Z

On 12/30/2025 9:01 AM, Bryan Green wrote:
> Ardres, Peter,
> 
> I have submitted a PR
> (https://github.com/anarazel/pg-vm-images/pull/131) to pg-vm-images to
> fix the python3.lib issue and will submit a patch to re-enable the
> Python Limited API on MSVC once done testing.
>

There are two problems regarding installing and finding python3.lib on
Windows (MSVC) builds:

1. We use SimpleInstall=1 as an option in the powershell script that
installs python on windows.  That is a minimal install and one of the
things it does not install...python3.lib. It installs python3XX.lib.

2. Meson will favor the python with the more complete version number.
We need to do a bit of work, but not much, in our top-level meson.build
for it to find the correct lib.

Once we have the python3.lib on our CI images by implementing the first
change then the second change can be done.

For those who may be interested in trying this locally--

Install python on windows using powershell:
(change versions and destination as you see fit)

1. Download: Invoke-WebRequest -Uri
"https://www.python.org/ftp/python/3.14.0/python-3.14.0-amd64.exe"
-OutFile "python-installer.exe"

In this step, you could pass SimpleInstall=1 in the ArgumentList and
python3.lib would not be installed.

2. Install without SimpleInstall=1:
Start-Process -Wait -FilePath "python-installer.exe" -ArgumentList
'/quiet', 'InstallAllUsers=1', 'PrependPath=1', 'TargetDir=c:\python\'

Then, in your local pg tree you need to remove the guard around
Py_LIMITED_API.

/*
 * Enable Python Limited API
 *
 * XXX currently not enabled on MSVC because of build failures
 */
#if !defined(_MSC_VER)
#define Py_LIMITED_API 0x03020000
#endif

At this point you will get build fails because of the meson issue, so in
the top-level meson.build file find the "Library: Python (for
'plpython') line and replace it's code block with the following:


###############################################################
# Library: Python (for plpython)
###############################################################

pyopt = get_option('plpython')
python3_dep = not_found_dep
if not pyopt.disabled()
  pm = import('python')
  python3_inst = pm.find_installation(python.full_path(), required: pyopt)
  if python3_inst.found()
    # For Limited API on MSVC, link against python3.lib instead of
python3XX.lib
    if host_system == 'windows' and cc.get_id() == 'msvc'
      python3_libdir = python3_inst.get_variable('prefix') / 'libs'
      python3_lib = cc.find_library('python3', dirs: python3_libdir,
required: pyopt)
      python3_dep = declare_dependency(
        include_directories:
include_directories(python3_inst.get_variable('prefix') / 'include'),
        dependencies: python3_lib,
      )
    else
      python3_dep = python3_inst.dependency(embed: true, required: pyopt)
    endif
    # Remove this check after we depend on Meson >= 1.1.0
    if not cc.check_header('Python.h', dependencies: python3_dep,
required: pyopt, include_directories: postgres_inc)
      python3_dep = not_found_dep
    endif
  endif
endif

Clear your meson cache and reconfigure if needed:

meson configure --clearcache build
meson setup --reconfigure build

Then build and test.

-- 
Bryan Green
EDB: https://www.enterprisedb.com