title: how to add new key with items as value to a nested dictionary
body: <p>I have this nested dictionary:</p>
  
  <pre><code>cities = {
  'new york city':{
      'country':'united states',
      'population': '8 million',
      'attraction':'statue of liberty'},
  }
  </code></pre>
  
  <p>... and I am trying to add a new key and a few key-value pair as items to the nested dict:</p>
  
  <pre><code>cities['white plains'] = {'white plains'}
  cities['white plains'] = {'country': 'united states'}
  cities['white plains'] = {'population':'60 thousand'}
  cities['white plains'] = {'attraction': 'kensico dam'}
  </code></pre>
  
  <p>... and its not working. (I am using 3.5)</p>