It has never been possible to combine a python part that installs packages using the python install script, with a part that installs python packages from the ubuntu archive. This causes many conflicts. However, on the plainbox plugin the install script is called with a prefix (python3 manage.py install --prefix=/providers/name), so this used to be doable without any conflicts. You could have a plainbox snap installing python dependencies from the archive. This week, in order to support python snaps in classic [1], we introduced to the python plugin a rewrite to /etc/python3.5/sitecustomize.py. So now there is a new conflict that does affect the plainbox plugin. If it tries to install a python deb from the archive it will bring ubuntu's default /etc/python3.5/sitecustomize.py and the snap will fail. To reproduce: $ git clone https://github.com/snapcore/snapcraft /tmp/snapcraft $ cd /tmp/snapcraft/integration_tests/snaps/plainbox-provider Modify the snapcraft.yaml adding at the end: stage-packages: [python3-petname] $ /tmp/snapcraft/bin/snapcraft Parts 'plainbox-local' and 'simple-plainbox-provider' have the followig file paths in common which have different contents: etc/python3.5/sitecustomize.py [1] https://github.com/snapcore/snapcraft/pull/1093/files