title: How to merge Python dict keys when their values are duplicates?
body: <p>This question is kind of hard to formulate, but let's say I have a dictionary.</p>
  <pre class="lang-py prettyprint-override"><code>{
     'a': 'hi',
     'b': 'hello',
     'c': 'hi'
  }
  </code></pre>
  <p>How can I re-arrange the keys and values to get a dictionary like this:</p>
  <pre class="lang-py prettyprint-override"><code>{
     'a and c': 'hi',
     'b': 'hello'
  }
  </code></pre>
  <p>Thank you for your help, I hope I was clear enough...</p>