The gnome-3-38 extension sets PYTHONPATH to its own python interpreter, seemingly overriding python plugin functionality and causing build errors. This seems to have a larger negative impact on python-based GTK 3 snaps (PyGObject), which requires both the python plugin and the gnone-3-38 extension (on core20). This apparent incompatibility between gnome-3-38 and the python plugin on core20 has driven developers to either use a custom python installation by overriding PYTHONPATH, or downgrade to core18 + gnome-3-34. Please refer to the following related forum topics for more details: https://forum.snapcraft.io/t/gnome-extension-conflicts-with-python-plugin/23921 https://forum.snapcraft.io/t/build-a-snap-with-any-version-of-python-i-want/10420 https://forum.snapcraft.io/t/pygobject-and-snap-problem/28477