During setup of stable Docker Engine repository in Ubuntu 18.04.02 Server Edition: cannot import name '_gi' from 'gi'

[marcoippolito]

Following the indications found here: https://docs.docker.com/install/linux/docker-ce/ubuntu/#install-using-the-repository
I'm trying to install Docker Engine in Ubuntu 18.04.02 Server Edition.

The first installation's steps went fine but I encountered this error message:

(base) marco@pc:~$ sudo add-apt-repository \ 
> "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
> $(lsb_release -cs) \
> stable"
Traceback (most recent call last):
  File "/usr/bin/add-apt-repository", line 11, in <module>
    from softwareproperties.SoftwareProperties import SoftwareProperties, 
shortcut_handler
  File "/usr/lib/python3/dist-packages/softwareproperties
/SoftwareProperties.py", line 67, in <module>
    from gi.repository import Gio
  File "/usr/lib/python3/dist-packages/gi/__init__.py", line 42, in 
<module>
    from . import _gi
ImportError: cannot import name '_gi' from 'gi' (/usr/lib/python3/dist-
packages/gi/__init__.py)

But import gi in python3 works fine:

(base) marco@pc:~$ python3
Python 3.7.3 (default, Mar 27 2019, 22:11:17) 
[GCC 7.3.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import gi
>>> 

How to solve the problem?

Marco