title: How to split my strings with re.split?
body: <p>I'm beginning my adventure with regular expressions.
  I'm interested in splitting specially formatted strings. If a letter is not inside parentheses it should become a different element of output list. Letters grouped inside parentheses should be put together.</p>
  
  <p>Samples:</p>
  
  <p>my string => wanted list</p>
  
  <ul>
  <li><code>"ab(hpl)x"</code> => <code>['a', 'b', 'hpl', 'x']</code></li>
  <li><code>"(pck)(kx)(sd)"</code> => <code>['pck', 'kx', 'sd']</code></li>
  <li><code>"(kx)kxx(kd)"</code> => <code>['kx', 'k', 'x', 'x', 'kd']</code></li>
  <li><code>"fghk"</code> => <code>['f', 'g', 'h', 'k']</code></li>
  </ul>
  
  <p>How can it be achieved with regular expressions and <code>re.split</code>?
  Thanks in advance for your help.</p>