=== Location of libbasix.so === The upstream installation of basix places libbasix.so in the lib subdir of the python module, /usr/lib/python3/dist-packages/basix/lib However, libbasix.so is not a python extension, it is a "private" library. dh_python3 will automatically rename it to libbasix.cpython-39-.so, but if that is done then the python extension _basixcpp.cpython-39-.so is not able to find "libbasix.so". libbasix.so can be left with its own name using "dh_python3 -Xlibbasix.so" or "dh_python3 --no-ext-rename" instead of renaming with an arch-specific suffix. In this case the python module will work for a given arch installation. But the filepath /usr/lib/python3/dist-packages/basix/lib/libbasix.so will then conflict in multiarch installations. For this reason, libbasix.so has been split out into libbasix-dev and libbasix0 as a conventional public shared library located in the standard library path /usr/lib/, and assigned SOVERSION=0 For consistency with the shared library, the header file basix.h has also been installed in libbasix-dev under the standard header path /usr/include, rather than inside the python module.