title: Make Dictionary with only keys?
body: <p>I need to make a dictionnary containing only keys.</p>
  
  <p>I cannot use <code>d.append()</code> as it is not a list, neither <code>setdefault</code> as it needs 2 arguments: a key and a value.</p>
  
  <p>It should work as the following:</p>
  
  <pre><code>d = {}
  </code></pre>
  
  <p>add "a":</p>
  
  <pre><code>d = {"a"}
  </code></pre>
  
  <p>add "b": </p>
  
  <pre><code>d = {"a", "b")
  </code></pre>
  
  <p>add "c" ...</p>
  
  <pre><code>#Final result is
  
  d = {"a", "b", "c"}
  </code></pre>
  
  <p>What is the code I need to get this result?
  Or is it another solution? Such as making a list. </p>
  
  <pre><code>l = ["a", "b", "c"] # and transform it into a dictionnary: d = {"a", "b", "c"} ?
  </code></pre>