SHELL

UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure. plt.show()

sudo apt-get install python3-tk

Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure.

apt-get install python-tk
or
apt-get install python3-tk

It's safer to apt-get install python-tk on your machine(s). 
(Works on Debian-derived distributions like for Ubuntu; 
refer to your package manager and package list on other 
distributions.)