For python version >3.6 NavigationToolbar2TkAgg-> NavigationToolbar2Tk

[jhgeeyang]

NavigationToolbar2TkAgg-> NavigationToolbar2Tk for gui.py

[AlbCa]

I follow this, fixing the issue would be great!

NavigationToolbar2TkAgg class was deprecated in version 2.2. In newer mpl versions, NavigationToolbar2Tk works exactly the same as NavigationToolbar2TkAgg, so it could be used a hack like the following:

try:
from matplotlib.backends.backend_tkagg import NavigationToolbar2TkAgg
except ImportError:
from matplotlib.backends.backend_tkagg import NavigationToolbar2Tk as NavigationToolbar2TkAgg

that would support both older matplotlib versions and newer ones.