title: Named regular expression group "(?P<group_name>regexp)": what does "P" stand for?
body: <p>In Python, the <code>(?P&lt;group_name&gt;…)</code> <a href="http://docs.python.org/library/re.html#regular-expression-syntax" rel="noreferrer">syntax</a> allows one to refer to the matched string through its name:</p>
  
  <pre><code>&gt;&gt;&gt; import re
  &gt;&gt;&gt; match = re.search('(?P&lt;name&gt;.*) (?P&lt;phone&gt;.*)', 'John 123456')
  &gt;&gt;&gt; match.group('name')
  'John'
  </code></pre>
  
  <p>What does "P" stand for?  I could not find any hint in the <a href="http://docs.python.org/library/re.html#regular-expression-syntax" rel="noreferrer">official documentation</a>.</p>
  
  <p>I would love to get ideas about how to help my students remember this syntax. Knowing what "P" does stand for (or might stand for) would be useful.</p>