Python packages are usually constructed to use either the flat or source layout
https://packaging.python.org/en/latest/discussions/src-layout-vs-flat-layout/

This repo presently uses the flat layout. This can cause problems if, for example, you want to use the surmise package installed in your venv but are running commands from the root of the repo. For instance, the nocoverage tox task can setup such a venv for you, but when it runs the task it can actually use content from the clone since it finds this in your current working directory.

We have seen this in the past where the .so cython file in the clone is getting used instead of the file in the installed package. This was popping up during testing of changes made for Issue #74.

Moses would like to update to the source layout.