title: Python OrderedDict: sort by tuple order?
body: <p>So I have this dictionary, which I'm converting to OrderedDict.  On conversion, I'd like to sort the OrderedDict by the order in which its keys appear in a separate tuple.  Any other values I'd like to append to the end of the OrderedDict.  Nonexistent keys in the ordering tuple should be ignored.</p>
  
  <p>I think I have most of it, but I'm having trouble wrapping my brain around the lambda sorted functions.  Can you help me iron it out?</p>
  
  <pre><code>from collections import OrderedDict
  
  d = {
      'spam': 'tasty',
      'subtitle': 'A Subtitle',
      'title': 'Test Title',
      'foo': 'bar',
  }
  
  key_order = ('title', 'subtitle', 'non_in_dictionary')
  ordered_dict = OrderedDict(sorted(d.items(), key=lambda ???? ))
  </code></pre>
  
  <p>should produce <code>ordered_dict</code>:</p>
  
  <pre><code>{
      'title': 'Test Title',
      'subtitle': 'A Subtitle',
      'spam': 'tasty',
      'foo': 'bar',
  }
  </code></pre>