My HPI repo is an example of using namespace packages as an plugin mechanism.

Both of them are installed as an editable package (like pip install -e ., which adds a egg file to ~/.local/lib/python3.9/site-packages/, and a line to ~/.local/lib/python3.9/site-packages/easy-install.pth.

Upsides:

• Any changes to either repo immediately update the local packages, no need to reinstall/re-run setup.py.
• Relative imports work across directory structures, no need to symlink.

Downsides:

• Requires quite a bit of domain knowledge on python packaging and troubleshooting to get work
• How name conflicts (i.e. if my HPI fork had a my.location subpackage and so did the upstream HPI, which are both installed as a namespace package) are handled are by the order of the paths in the easy-install.pth, e.g.:

cat ~/.local/lib/python3.9/site-packages/easy-install.pth
/home/sean/Repos/HPI
/home/sean/Repos/HPI-to-master

means that HPI overrides any namespace packages in HPI-to-master.

The fact that it overrides is great! Since it means I can overwrite files in the upstream repo without having to maintain a fork and having to deal with merging changes back and forth. But, sometimes when re-installing (or for some reason I can’t seem to find) easy-install.pth gets messed with, and I have to manually fix it. Perhaps a tool should be written to handle this…