title: Iterating over key and value of defaultdict dictionaries
body: <p>The following works as expected:</p>
  
  <pre><code>d = [(1,2), (3,4)]
  for k,v in d:
    print "%s - %s" % (str(k), str(v))
  </code></pre>
  
  <p>But this fails:</p>
  
  <pre><code>d = collections.defaultdict(int)
  d[1] = 2
  d[3] = 4
  for k,v in d:
    print "%s - %s" % (str(k), str(v))
  </code></pre>
  
  <p>With:</p>
  
  <pre><code>Traceback (most recent call last):  
   File "&lt;stdin&gt;", line 1, in &lt;module&gt;  
  TypeError: 'int' object is not iterable 
  </code></pre>
  
  <p>Why? How can i fix it?</p>