title: Counting number of different characters in a word
body: <p>I am trying to think of a program to count the number of different characters in a word in Python. </p>
  
  <p>For example:</p>
  
  <ul>
  <li><p>Given the input:</p>
  
  <pre><code>('Banana') 
  </code></pre></li>
  <li><p>Expected output: </p>
  
  <pre><code>3
  </code></pre></li>
  </ul>
  
  <p>How can I use a <code>while</code> or <code>for</code> loop to do this?</p>
  
  <p>Thanks </p>