Filing on behalf of a user. $ snapcraft --shell-after Launching a VM. Skipping pull copy-stuff (already ran) Skipping pull desktop-gtk3 (already ran) Skipping pull rubber-band-async (already ran) Skipping build copy-stuff (already ran) Skipping build desktop-gtk3 (already ran) Copying needed target link from the system /lib/x86_64-linux-gnu/liblzma.so.5.2.2 Copying needed target link from the system /lib/x86_64-linux-gnu/libpcre.so.3.13.3 Cleaning later steps and re-building rubber-band-async ('override-build' property changed) /root/parts/rubber-band-async/install/usr/bin/python3: No module named pip Failed to run '/root/parts/rubber-band-async/install/usr/bin/python3 -m pip wheel --no-index --find-links /root/parts/rubber-band-async/python-packages --wheel-dir /tmp/tmpytyegx1n --requirement /root/project/requirements-linux.txt https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-18.04/wxPython-4.0.4-cp36-cp36m-linux_x86_64.whl': Exited with code 1. Run the same command again with --debug to shell into the environment if you wish to introspect this failure. An error occurred when trying to execute 'sudo -i env SNAPCRAFT_HAS_TTY=True snapcraft snap' with 'multipass': returned exit code 2. I would think this user error if not for the fact that pip comes from the plugin itself, so on first inspection it looks like snapcraft is cleaning the pip installation but not reinstalling it prior to running again. Here's the snapcraft.yaml: name: rubber-band-async # you probably want to 'snapcraft register <name>' version: '0.1' # just for humans, typically '1.2+git' or '1.3.2' summary: Rubberband wxPython app with wxasync clock # 79 char long summary description: | ... grade: devel # must be 'stable' to release into candidate/stable channels confinement: strict # use 'strict' once you have the right plugs and slots base: core18 apps:    rubber-band-async:        command: desktop-launch python3 $SNAP/rubber_band_async.py        plugs: [x11, unity7, pulseaudio, home, gsettings, network]        environment:            LD_LIBRARY_PATH: $LD_LIBRARY_PATH:$SNAP/usr/lib/x86_64-linux-gnu/pulseaudio    python:        command: usr/bin/python -vvv    python3:        command: usr/bin/python3 -vvv    python-nopath:        command: python -vvv    python3-nopath:        command: python3 -vvv    report:        command: python3 $SNAP/report_snap_env.py    report-hack:        command: python3 $SNAP/report_snap_env.py        environment:          PATH: $PATH:$SNAP/bin/          PYTHONPATH: $PYTHONPATH:$SNAP/lib/python3.6/site-packages parts:  desktop-gtk3:    build-packages:    - build-essential    - libgtk-3-dev    make-parameters:    - FLAVOR=gtk3    plugin: make    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git    source-subdir: gtk    stage-packages:    - libxkbcommon0    - ttf-ubuntu-font-family    - dmz-cursor-theme    - light-themes    - adwaita-icon-theme    - gnome-themes-standard    - shared-mime-info    - libgtk-3-0    - libgdk-pixbuf2.0-0    - libglib2.0-bin    - libgtk-3-bin    - unity-gtk3-module    - libappindicator3-1    - locales-all    - xdg-user-dirs    - ibus-gtk3    - libibus-1.0-5    - fcitx-frontend-gtk3  copy-stuff:    plugin: dump    source: .  rubber-band-async:    # See 'snapcraft plugins'    plugin: python    python-version: python3    source: .    stage-packages:        # - libc6        - libssl-dev        - libjpeg-dev        - libtiff-dev        - libsdl1.2-dev        - libnotify-dev        - freeglut3        - ibus-gtk3        - libwebkitgtk-3.0-0        - zlib1g        - libsm6        - libpulse0        - libslang2    #after: [desktop-gtk3]    python-packages:        #- https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-18.04/wxPython-4.0.4-cp37-cp37m-linux_x86_64.whl        - https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-18.04/wxPython-4.0.4-cp36-cp36m-linux_x86_64.whl    requirements:        - /root/project/requirements-linux.txt