title: Find longest (string) key in dictionary
body: <p>This question is similar to <a href="https://stackoverflow.com/questions/4321160/python-find-longest-most-words-key-in-dictionary">Python - Find longest (most words) key in dictionary</a> - but I need the pure number of characters.</p>
  
  <p>Example input:</p>
  
  <pre><code>d = {'group 1': 1, 'group 1000': 0}
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>10
  </code></pre>