title: Way to ignore case in iteration of glob
body: <p>Is there a simpler way to do the following to iterate over <code>xls</code> files regardless of capitalization?</p>
  
  <pre><code>for file in [glob.glob(os.path.join(dir, '*.xls')), glob.glob(os.path.join(dir, '*.XLS'))]:
  </code></pre>