title: Fastest way to convert a dict's keys & values from `unicode` to `str`?
body: <p>I'm receiving a dict from one "layer" of code upon which some calculations/modifications are performed before passing it onto another "layer". The original dict's keys &amp; "string" values are <code>unicode</code>, but the layer they're being passed onto only accepts <code>str</code>.</p>
  
  <p>This is going to be called often, so I'd like to know what would be the fastest way to convert something like:</p>
  
  <pre><code>{ u'spam': u'eggs', u'foo': True, u'bar': { u'baz': 97 } }
  </code></pre>
  
  <p>...to:</p>
  
  <pre><code>{ 'spam': 'eggs', 'foo': True, 'bar': { 'baz': 97 } }
  </code></pre>
  
  <p>...bearing in mind the non-"string" values need to stay as their original type.</p>
  
  <p>Any thoughts?</p>