title: How to only do string manupilation on column of pandas that have 4 digits or less?
body: <p>I have df that looks like this:</p>
  
  <pre><code>   numbers
  0      111
  1    22222
  2     3423
  </code></pre>
  
  <p>I want to apply a <code>0</code> to the beginning of any 4digit number, how do I do this? </p>
  
  <p>New df should look like this:</p>
  
  <pre><code>   numbers
  0      111
  1    22222
  2    03423
  </code></pre>