title: Python PANDAS: Conditionally Insert Character in String Field
body: <p>What would be the best way to insert a character conditionally in a PANDAS string field with the following criteria:</p>
  
  <ol>
  <li>Insert a "." after the first 3 numeric characters from the left (ignore letters)</li>
  <li><p>Do not add a "." if there are no additional characters trailing</p>
  
  <pre><code>96501
  E0000
  V909
  965
  </code></pre>
  
  <p>Becomes</p>
  
  <pre><code>965.01
  E000.0
  V909
  965
  </code></pre></li>
  </ol>