title: how do I add fields to a namedtuple?
body: <p>I am working with a list of namedtuples. I would like to add a field to each named tuple after it has already been created. It seems I can do that by just referencing it as an attribute (as in <code>namedtuple.attribute = 'foo'</code>), but then it isn't added to the list of fields. Is there any reason why I shouldn't do it this way if I don't do anything with the fields list? Is there a better way to add a field?</p>
  
  <pre><code>&gt;&gt;&gt; from collections import namedtuple
  &gt;&gt;&gt; result = namedtuple('Result',['x','y'])
  &gt;&gt;&gt; result.x = 5
  &gt;&gt;&gt; result.y = 6
  &gt;&gt;&gt; (result.x, result.y)
  (5, 6)
  &gt;&gt;&gt; result.description = 'point'
  &gt;&gt;&gt; (result.x, result.y, result.description)
  (5, 6, 'point')
  &gt;&gt;&gt; result._fields
  ('x', 'y')
  </code></pre>