title: iterate over only two keys of python dictionary
body: <p>What is the pythonic way to iterate over a dictionary with a setup like this:</p>
  
  <pre><code>dict = {'a': [1, 2, 3], 'b': [3, 4, 5], 'c': 6}
  </code></pre>
  
  <p>if I only wanted to iterate a for loop over all the values in <code>a</code> and <code>b</code> and skip <code>c</code>.  There's obviously a million ways to solve this but I'd prefer to avoid something like:</p>
  
  <pre><code>for each in dict['a']:
      # do something
      pass
  for each in dict['b']:
      # do something
      pass
  </code></pre>
  
  <p>of something destructive like:</p>
  
  <pre><code> del dict['c']
   for k,v in dict.iteritems():
       pass
  </code></pre>