title: Filter nested dictionary in python based on key values
body: <p>How do I filter a nested dictionary in python based on key values:</p>
  
  <pre><code>d = {'data': {'country': 'US', 'city': 'New York', 'state': None},
       'tags': ['US', 'New York'],
       'type': 'country_info',
       'growth_rate': None
       }
  </code></pre>
  
  <p>I want to filter this dictionary to eliminate NoneType values so the resulting dict should be:</p>
  
  <pre><code>d = {'data': {'country': 'US', 'city': 'New York'},
       'tags': ['US', 'New York'],
       'type': 'country_info',
       }
  </code></pre>
  
  <p>Also, the dict can have multiple levels of nesting. I want to remove all NoneType values from the dict.</p>