title: Adding Items to Python Dictionary
body: <p>I may have understood this wrong but looking at the examples found in "Learning Python" by O'Reilly I tried to do the following:</p>
  
  <pre><code>&gt;&gt;&gt; d={}
  &gt;&gt;&gt; d['h']='GG'
  &gt;&gt;&gt; d['f']='JJ'
  &gt;&gt;&gt; d['h']='PP'
  &gt;&gt;&gt; print d
  {'h': 'PP', 'f': 'JJ'}
  </code></pre>
  
  <p>Now instead of the 'key' <code>'h'</code> having two entries <code>'GG'</code> and <code>'PP'</code> it only has the last entry, the last one replacing the first one.
  I want BOTH in the same key.</p>
  
  <pre><code>&gt;&gt;&gt; d['h']+='RR'
  &gt;&gt;&gt; print d
  {'h': 'PPRR', 'f': 'JJ'}
  </code></pre>
  
  <p>Again this doesn't work, what I wanted was not a concatenated string but comma-separated entires. </p>
  
  <p>I am confused why this does not work.</p>