title: Pandas append returns DF with NaN values
body: <p>I'm appending data from a list to pandas df. I keep getting NaN in my entries.</p>
  
  <p>Based on what I've read I think I might have to mention the data type for each column in my code.</p>
  
  <pre><code>dumps = [];features_df = pd.DataFrame()
  for i in range (int(len(ids)/50)): 
      dumps = sp.audio_features(ids[i*50:50*(i+1)])
      for i in range (len(dumps)):
          print(list(dumps[0].values()))
          features_df = features_df.append(list(dumps[0].values()), ignore_index = True)
  </code></pre>
  
  <p>Expected results, something like-<br>
  [0.833, 0.539, 11, -7.399, 0, 0.178, 0.163, 2.1e-06, 0.101, 0.385, 99.947, 'audio_features', '6MWtB6iiXyIwun0YzU6DFP', 'spotify:track:6MWtB6iiXyIwun0YzU6DFP', '<a href="https://api.spotify.com/v1/tracks/6MWtB6iiXyIwun0YzU6DFP" rel="nofollow noreferrer">https://api.spotify.com/v1/tracks/6MWtB6iiXyIwun0YzU6DFP</a>', '<a href="https://api.spotify.com/v1/audio-analysis/6MWtB6iiXyIwun0YzU6DFP" rel="nofollow noreferrer">https://api.spotify.com/v1/audio-analysis/6MWtB6iiXyIwun0YzU6DFP</a>', 149520, 4]
  for one row.
  Actual-<br>
     danceability  energy       ...        duration_ms  time_signature<br>
  0            NaN     NaN       ...                NaN             NaN<br>
  1            NaN     NaN       ...                NaN             NaN<br>
  2            NaN     NaN       ...                NaN             NaN<br>
  3            NaN     NaN       ...                NaN             NaN<br>
  4            NaN     NaN       ...                NaN             NaN<br>
  5            NaN     NaN       ...                NaN             NaN </p>
  
  <p>For all rows            </p>