Debugging why `import google.protobuf` wasn't working inside a snap, I found that snapcraft only puts $SNAP/lib/python*/site-packages into site.addsitedir(). As I was using pip inside a scriptlet without additional environment variables or command line parameters, it was installing the modules to $SNAP/usr/lib/python*/site-packages. This meant that python was looking in the wrong place for protobuf-3.4.0-py2.7-nspkg.pth. Can we include $SNAP/usr/lib in a list fed to site.addsitedir()?