title: Package 'python-tk' has no installation candidate
body: <p>I am trying it install <strong>Tinker</strong> on my <strong>Ubuntu 17.04</strong> but some how it does not seem working, I have used all these command on the terminal</p>
  
  <pre><code>sudo apt-get install update
  sudo apt-get install upgrade    
  sudo apt-get install python-tk
  sudo apt-get install python3-tk
  </code></pre>
  
  <p>Every time I am getting :</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Package python-tk is not available, but is referred to by another package.
  This may mean that the package is missing, has been obsoleted, or
  is only available from another source
  
  E: Package 'python-tk' has no installation candidate
  </code></pre>