"UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure." when plotting figure with pyplot on Pycharm

Question

I am trying to plot a simple graph using pyplot, e.g.:

import matplotlib.pyplot as plt
plt.plot([1,2,3],[5,7,4])
plt.show()

but the figure does not appear and I get the following message:

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

I saw in several places that one had to change the configuration of matplotlib using the following:

import matplotlib
matplotlib.use('TkAgg')
import matplotlib.pyplot as plt

I did this, but then got an error message because it cannot find a module:

ModuleNotFoundError: No module named 'tkinter'

Then, I tried to install "tkinter" using pip install tkinter (inside the virtual environment), but it does not find it:

Collecting tkinter
  Could not find a version that satisfies the requirement tkinter (from versions: )
No matching distribution found for tkinter

I should also mention that I am running all this on Pycharm Community Edition IDE using a virtual environment, and that my operating system is Linux/Ubuntu 18.04.

I would like to know how I can solve this problem in order to be able to display the graph.

Answer 1

Solution 1: is to install the GUI backend tk

I found a solution to my problem (thanks to the help of ImportanceOfBeingErnest).

All I had to do was to install tkinter through the Linux bash terminal using the following command:

sudo apt-get install python3-tk

instead of installing it with pip or directly in the virtual environment in Pycharm.

Solution 2: install any of the matplotlib supported GUI backends

• solution 1 works fine because you get a GUI backend... in this case the TkAgg
• however you can also fix the issue by installing any of the matplolib GUI backends like Qt5Agg, GTKAgg, Qt4Agg, etc
  • for example pip install pyqt5 will fix the issue also

NOTE:

• usually this error appears when you pip install matplotlib and you are trying to display a plot in a GUI window and you do not have a python module for GUI display.
• The authors of matplotlib made the pypi software deps not depend on any GUI backend because some people need matplotlib without any GUI backend.