title: Adding entries to list in dictionary
body: <p>I have a question about the following:
  Let's say I have a datastructure like this</p>
  
  <p><code>shelfFile['Test']</code> which is a dictionary in a shelve file.
  I added some values to it using <code>shelfFile['Test'] = {"January":["Test1","Test2"]}</code>
  Now, when I want to add Test3 using <code>shelfFile['Test']['January'].append()</code> it does not work, it returns only the original values "Test1" and "Test2". I have also tried using</p>
  
  <pre><code>shelfFile['test'].setdefault('January', []).append('Test3')
  </code></pre>
  
  <p>but this does not work as well, is this due to any mutability of the dictionary/tuple? Maybe someone can recommend some alternative data structure which is more suitable? The "Test" entry is permanent, the month entries are permanent as well although every month a new entry is added. The "Test1", "Test2" can be added or removed at any time.</p>
  
  <p>Any help is appreciated!</p>