[Python] Can't load C++ unit test module with python 3.10 on windows (using boost 1.75.0)

I have a challenging tricky issue managing the unit tests of my C++ project in Python.

The project

The project is a big one, strongly relying on boost, with several dlls/so files and the funcitonnalities are exported to python. So I can't copy the code and it's hard to extract a minimal sample from all of that. Moreover I'm pretty sure this is more a configuration problem than a code issue. I'll give a sample of code though, concerning the critical part.

The problem

I have an unit test routine in C++ that I can use in python. It works well for both python 3.8 and 3.9. It also works with python 3.10 on Linux, but I get the following message on Windows:

<class 'ImportError'> : DLL load failed while importing UnitTestTools_4_1_0_0_beta_x64: The specified module was not found.


I checked the dependancies and they all exist and their locations are all listed in sys.path. I use sys.path.insert(0, dirPath) to add the directory containing the dll/so and pyd files. I also checked with DependenciesGui.exe

Moreover, I can use all the functionalities of my project, i.e. I can import other files and call the functions they contain. Only the unit test on windows with Python 3.10 fails to import the related module.

The configuration

C++ side, I'm using boost 1.75.0 and build the project with visual studio 2019 on Windows and gcc 9.4 on Linux. The only libraries I need to interface C++ and python are boost_python and boost_numpy.

I built boost dlls from sources (with some patches to manage newest python requirements), with dedicated Anaconda virtual environments for each version of python I need to support (3.8, 3.9 and 3.10).

Python side, when I use my libraries in python, I use the default Anaconda environment configured during the installation. I won't list all the modules installed (I can provide more if necessary) but here a comparison of python and numpy versions:

| Windows | Linux
---------------+---------|-------
Python version | 3.9.13 | 3.9.7
Numpy version | 1.24.1 | 1.26.3
---------------+---------|-------
Python version | 3.10.9 | 3.10.9
Numpy version | 1.23.5 | 1.23.5


I also tried with several version of numpy for Windows/Python 3.10 (1.24.1 for instance).

I found that there was a change in the ABI between 3.9 and 3.10 but I don't think this is the reason of my problem since it works on linux.

Solving attempts

As a summary of all my attempts to solve the problem, here is what I did:

• check that my pyd's dependancies exist
• check the content of sys.path
• build boost 1.75.0 with the same numpy version for all python version
• configure a python environment with several versions of numpy

Some sample of code

Just in case it helps, I copy a part of the code concerning the unit test module export

pythonMajorVersion = sys.version_info.major
pythonMinorVersion = sys.version_info.minor
pythonVersionSubDir = "Python" + str(pythonMajorVersion) + "_" + str(pythonMinorVersion)

# add of binary directory to path
binaryDir = getBinDir() # Directory where the dlls are stored
if not binaryDir in sys.path:
sys.path.insert(1, binaryDir)
if os.name == "nt":
os.environ["PATH"] = os.environ["PATH"] + ";" + binaryDir
# The python pyds are located in a specific subdirectory called "Python3_8", "Python3_9" or "Python3_10" depending on the python I'm using
pythonBinaryDir = os.path.join(binaryDir, pythonVersionSubDir)
if not pythonBinaryDir in sys.path:
sys.path.insert(1, pythonBinaryDir)
if os.name == "nt":
os.environ["PATH"] = os.environ["PATH"] + ";" + pythonBinaryDir

# Generate the full module name, for instance 'PyUnitTestTools_1_0_0_0_x64', 1.0.0.0 being the version number
unitTestModuleName = getLibName("PyUnitTestTools")

try:
self.unittest = import_module(unitTestModuleName)
except:
print("Failed to initialize unit test framework\n" + str(sys.exc_info()[0]) + " : " + str(sys.exc_info()[1]))


I'm not sure adding the libraries directories to both sys.path and os.environ["PATH"] is necessary but I tried just in case it could help.

Can't I load the unit test module in this specific configuration (Windows, Python 3.10)?

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