title: "UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure." when plotting figure with pyplot on Pycharm
body: <p>I am trying to plot a simple graph using pyplot, e.g.:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  plt.plot([1,2,3],[5,7,4])
  plt.show()
  </code></pre>
  
  <p>but the figure does not appear and I get the following message:</p>
  
  <pre><code>UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure.
  </code></pre>
  
  <p>I saw in several places that one had to change the configuration of matplotlib using the following:</p>
  
  <pre><code>import matplotlib
  matplotlib.use('TkAgg')
  import matplotlib.pyplot as plt
  </code></pre>
  
  <p>I did this, but then got an error message because it cannot find a module:</p>
  
  <pre><code>ModuleNotFoundError: No module named 'tkinter'
  </code></pre>
  
  <p>Then, I tried to install "tkinter" using <code>pip install tkinter</code> (inside the virtual environment), but it does not find it:</p>
  
  <pre><code>Collecting tkinter
    Could not find a version that satisfies the requirement tkinter (from versions: )
  No matching distribution found for tkinter
  </code></pre>
  
  <p>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.</p>
  
  <p><strong>I would like to know how I can solve this problem in order to be able to display the graph.</strong></p>