ImportError: DLL load failed: The specified module could not be found for custom built pkg using Swig & CMake

Question

I want to make a Python Package for win_amd64 (Windows x64) of cpp files. I have used Swig to wrap them into python and then used setuptools to build it. I have made CMakeLists.txt files to do all this actions. Note: I am using x86_64-w64-mingw32 cross-compiler to build this in linux machine

Tools Used & its Version:

• Swig Version: 4.1.1
• CMake Version: 3.27
• Python Version: 3.9.18 (linux) - to run setuptools
• Cross Compiler Toolchain: x86_64-w64-mingw32
• Linux Distro & Version: Ubuntu 20.04
• Python 3.9 Windows AMD64 - dev.msi pkg (wget'ed the dev.msi and msiextracted it to local folder)

Note: I can build the python pkg for linux-x86_64 (linux 64) for all of Python3.6 and above, but for windows I can only build for Python3.6 (By using the library libpython36.a) but with later version for win_amd64 I had to use the libpython39.lib (Lib based libraries)

What happens now:

1. I can build the whl file for win_amd64 successfully. CMake can make the .dll and setuptools wrapped it well

2. On installing this on windows Python3.9 x64, it installs without any warning

3. But when I try to import the main module, it throws

   import sample # name of the module
   # Error below
   Traceback:
   from . import _sample_swig
   ImportError: DLL load failed: The specified module could not be found.ImportError: DLL load failed: The specified module could not be found.`
   

Project Setup:

1. Swig File

   FIND_PACKAGE(SWIG REQUIRED)
   INCLUDE(${SWIG_USE_FILE})
   CMAKE_MINIMUM_REQUIRED(VERSION 3.16)
   SET(PYTHON_MODULE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/sample)
   set(PYTHON_EXECUTABLE python${PYTHON_BUILD_VERSION})
   if (${BUILD_PLATFORM} MATCHES "Windows")
       set(CMAKE_SYSTEM_NAME Windows)
       set(CMAKE_C_COMPILER   /usr/bin/x86_64-w64-mingw32-gcc)
       set(CMAKE_CXX_COMPILER /usr/bin/x86_64-w64-mingw32-g++)
       set(PYTHON_LIBRARY /home/developer/workspace/69/py39/libs/python.lib)
       set(PYTHON_INCLUDE_DIR /home/developer/workspace/69/py39/include)
       set(TARGET_EXTENSION "pyd")
       set(CMAKE_FIND_ROOT_PATH /opt/win_cross_compile_libs)
   
   ELSE()
       set(CMAKE_C_COMPILER /usr/bin/gcc)
       set(CMAKE_CXX_COMPILER /usr/bin/g++)
       set(TARGET_EXTENSION "so")
       set(PythonLibs_DIR /usr/lib/x86_64-linux-gnu/)
       set(CMAKE_FIND_ROOT_PATH /usr/lib/x86_64-linux-gnu/)
   ENDIF()
   project(sample LANGUAGES CXX)
   set(CMAKE_LANGUAGE_COMPILER ${CMAKE_CXX_COMPILER})
   FIND_PACKAGE(Python3 COMPONENTS Interpreter Development)
   FIND_PACKAGE(PythonLibs)
   INCLUDE_DIRECTORIES(${PYTHON_INCLUDE_DIRS} ${PROJECT_SOURCE_DIR}/include)
   message(STATUS "Py Libs: ${PYTHON_LIBRARIES}")
   message(STATUS "Add. Linking Flags: ${ADD_LINK_FLAGS}")
   message(STATUS "Python Incl Dir: ${PYTHON_INCLUDE_DIR}")
   message(STATUS "Python Module: ${PYTHON_MODULE_DIR}")
   message(STATUS "Machine: ${CMAKE_SYSTEM_NAME}")
   set(PythonLibs_DIR "/usr/lib/x86_64-linux-gnu/")
   set_property(SOURCE include/sample.i PROPERTY CPLUSPLUS ON)
   file(GLOB SRC_FILES ${PROJECT_SOURCE_DIR}/src/*.cpp)
   swig_add_library(sample_swig TYPE SHARED
             LANGUAGE python
             OUTPUT_DIR ${PYTHON_MODULE_DIR}
             OUTFILE_DIR src
             SOURCES include/sample.i ${SRC_FILES}
             )
   SWIG_LINK_LIBRARIES(sample_swig ${PYTHON_LIBRARIES})
   add_custom_command(
   TARGET _sample_swig POST_BUILD
   COMMAND ${CMAKE_COMMAND} -E copy
        _sample_swig.${TARGET_EXTENSION}
        ${PYTHON_MODULE_DIR}/_sample_swig.${TARGET_EXTENSION}
   )
   
   INSTALL(TARGETS _sample_swig LIBRARY DESTINATION sample)
   

2. Interface file used for swig:

   %module arithmetic_operator
   %{
       #include "addition.h"
   %}
   %include "addition.h"
   %include "stdint.i"`
   

3. Header file:

   # include <iostream>
   using namespace std;
   
   int addition_fn(int a, int b)
   {
       return (a+b);`
   }
   

4. CPP File:

   # include <iostream>
   using namespace std;
   const int MAX_ADDABLE = 50;
   int main()
   {
       cout<<"Hello World\n";
   }
   

5. Setup.py:

   from skbuild import setup
   
   setup(
   name='sample',
   version='0.1.0',
   description='Sample',
   cmake_with_sdist=True,
   packages=['sample'],
   python_requires=">=3.6",
   include_package_data=True,
   zip_safe=False
   )
   

Using os.add_dll_directory(<dll folder location (site-packages/sample)>) as the Python3.8 and above only loads from trusted sources even though overwritten by PYTHONPATH - Doesn't work

Answer 1

Wasn't able to figure it out for a month.

I finally fixed this by moving my x86_64-w64-mingw32-g++ which was on 9.0.x on Ubuntu 20.04 to compiler x86_64-w64-mingw32-g++-posix with GCC version 10-posix 20220113 (GCC) on Ubuntu-22.04

Seems like the latest GCC will seemingly handle Windows Python 3.8+ DLL based handles when using Shared Libraries