ModuleNotFoundError: No module named 'tkcalendar'
Make sure that when you're running your file you use python3. I was having the same issue because I just used python and it reverted to python2
I had this same problem and since I was new to this I searched everywhere and couldn't find a solution that worked. Finally I moved the cursor to line 'from tkcalendar import *' (right over tkcalendar) and a pop-up gave me a link to install tkcalendar. That seemed to be all there was to it. I tried pip install tkcalendar several times and even pip3 to see what it would do. Nothing worked except for what I just mentioned above.