title: Sorting Lists with numerals
body: <p>If I have a list that all strings but with numerals : </p>
  
  <pre><code>a = ['0.01um', 'Control', '0.1um', '0.05um']
  </code></pre>
  
  <p>If I sort the list it looks like this </p>
  
  <pre><code>a.sort()
  print(a)
  ['0.01um', '0.05um', '0.1um', 'Control']
  </code></pre>
  
  <p>How can I make it sort with so the strings starting with letters come before the strings starting with numbers, but the numbers are still ordered from smallest to biggest.  For instance : </p>
  
  <pre><code>['Control', '0.01um', '0.05um', '0.1um']
  </code></pre>