ImportError: No module named ‘Tkinter’

For some reason, I can’t use the Tkinter or tkinter module.
After running the following command in the python shell

import Tkinter

or

import tkinter

I got this error

ModuleNotFoundError: No module named ‘Tkinter’

or

ModuleNotFoundError: No module named ‘tkinter’

What could be the reason for and how can we solve it?