title: How to use text strip() function?
body: <p>I can strip numerics but not alpha characters:</p>
  
  <pre><code>&gt;&gt;&gt; text
  '132abcd13232111'
  
  &gt;&gt;&gt; text.strip('123')
  'abcd'
  </code></pre>
  
  <p>Why the following is not working?</p>
  
  <pre><code>&gt;&gt;&gt; text.strip('abcd')
  '132abcd13232111'
  </code></pre>