Note2: After installing the Nvidia driver for my graphics card different: via "sudo apt-get install nvidia-390", I always get the error in python "ModuleNotFoundError: No module named 'tkinter'", but of course tkinter is installed. So currently I can not use python... it was the same error in ubuntu 16.04 and the reason why I updated. Hoped it would work in 18.04... I opened a new post for this: After installing Nvidia driver I get "ModuleNotFoundError: No module named 'tkinter'" error in Python3