title: Get parents keys from nested dictionary
body: <p>From the following nested dictionary, how can I get every parent dictionary key of <code>'value4ac'</code>? By starting the <code>'value4ac'</code> value, I want to get <code>'key4'</code>, <code>'key4a'</code>, <code>'Key4ac'</code>.</p>
  
  <pre><code>example_dict = { 'key1' : 'value1',
                   'key2' : 'value2',
                   'key3' : { 'key3a': 'value3a' },
                   'key4' : { 'key4a': { 
                                           'key4aa': 'value4aa',
                                           'key4ab': 'value4ab',
                                           'key4ac': 'value4ac'
                                       },
                              'key4b': 'value4b'
                             }
                     } 
  </code></pre>