Installing & configuring ISSO under Debian Trixie
For some reasons ISSO stopped working after I upgraded to Debian Trixie. Steps which weren't necessary when I first wrote my post Integrating Isso into Bludit via Apache2 and WSGI.
Take this post as an addition to the previous one.
Troubleshooting steps for Debian Trixie
ModuleNotFoundError: No module named 'pkg_resources'
This one was solved with an pip install setuptools. Despite being already installed and shown as installed when pip list is executed.
ModuleNotFoundError: No module named '_cffi_backend'
This one still baffles me. pip list shows the cffi module as being installed. However under Debian the package python3-cffi-backend must be installed for me. I think that I maybe hadn't all needed ffi packages installed, so the compiled /opt/your-venv-here/lib/python3.13/site-packages/_cffi_backend.cpython-313-x86_64-linux-gnu.so isn't fully working. Have to investigate.
If these two things are taken care of ISSO works fine under Debian Trixie.
Conclusion
All in all I suspect that I did get those errors as I did an in-place dist-upgrade from bullseye to bookworm to trixie on one afternoon. No fresh re-install as I currently lack the same for this.