I suddenly had a problem on the laptop (ubuntu 18.04, Bionic), and I’ve seen similar problems on Cinnamon. One manifestation is that when I try to start terminal using the gnome-terminal.desktop app, i.e. the icon in the dock, the launch fails, with no stated reason. A look in the log reveals a problem in Python loading _gi.
I resolved to look at it later. I was able to start the terminal from the desktop by right clicking, and open terminal.
Later I had a similar problem trying to launch gnome-tweak. It failed in the same way, trying to start up the python app it attempted to load _gi.
I have only the vaguest clue what is going on here. I looked at the python code. Indeed they are attempting:
From . import _gi.
And the directory /usr/lib/python3/dist-packages/gi does not have a library named _gi. It does however have two library files:
_gi.cpython-36m-x86_64-linux-gnu.so and _gi_cairo.cpython-36m-x86_64-linux-gnu.so
Perusing the net, I find some suggestion that these libraries, with the 36m designation are somehow specific to or found by Python 3.6, and that if I want this to work under Python 3.7, I have to copy these files, and change 36m to 37m.
Ok, what have I got to lose? I did that simple thing – with just a simple copy in the above named directory. Lo and behold, it fixed the symptom that I was experiencing.
I don’t really like fixing things with magic when I don’t know what is happening, but now is not the time to go on a voyage of discovery with Python.