title: Extract list of JSON objects in string form from Pandas Dataframe column
body: <p>I have a perfectly normal pandas dataframe which I create after loading this dataset: <a href="https://www.kaggle.com/tmdb/tmdb-movie-metadata/data" rel="nofollow noreferrer">https://www.kaggle.com/tmdb/tmdb-movie-metadata/data</a></p>
  
  <p>As you can see, the genres column contains a nested structure which appears to be a list of dictionaries, or json objects depending on how you see it? The keys of these dictionaries are 'id' and 'name'.</p>
  
  <p>Anyways, I have tried everything including transforming the column into a json with tojson(), or using pandas json_normalize() method without any luck. </p>
  
  <p>If I use json_normalize() I get an AttributeError: 'str' object has no attribute 'itervalues':</p>
  
  <pre><code>pd.io.json.json_normalize(obj_movies['genres'], meta = ['id','name']) 
  </code></pre>
  
  <p>In reality, my goal would be to parse this list to create a set of unique  genres names for each row...</p>