title: python group(0) meaning
body: <p>What is the exact definition of group(0) in 
  re.search? </p>
  
  <p>Sometimes the search can get complex and I would like to know what is the supposed group(0) value by definition? </p>
  
  <p>Just to give an example of where the confusion comes, consider this matching. The printed result is only <code>def</code>. So in this case group(0) didn't return the entire match. </p>
  
  <pre><code> m = re.search('(?&lt;=abc)def', 'abcdef')
  &gt;&gt;&gt; m.group(0)
  def
  </code></pre>