title: What does "?:" mean in a Python regular expression?
body: <p>Below is the Python regular expression. What does the <code>?:</code> mean in it?  What does the expression do overall?  How does it match a MAC address such as "<code>00:07:32:12:ac:de:ef</code>"?</p>
  
  <pre><code>re.compile(([\dA-Fa-f]{2}(?:[:-][\dA-Fa-f]{2}){5}), string)  
  </code></pre>