title: Why can't I install modules using pip
body: <p>I can't install any module. For example, the command</p>
  
  <pre><code>pip install Pillow
  </code></pre>
  
  <p>gives the following error</p>
  
  <pre><code>Collecting Pillow
    Could not find a version that satisfies the requirement Pillow (from versions: )
  No matching distribution found for Pillow
  </code></pre>
  
  <p>I have a mac with two operating systems. One is macOS Sierra and the other is Linux Mint. Both give exactly the same error.</p>