title: Cannot append Data with panas.append function
body: <p>following code is not running, I have no guess why.</p>
  <pre><code>import pandas as pd
  import numpy as np
  
  df = pd.DataFrame(columns=['Interval', 'Weight'])
  intersection = np.array([1,2,3,4,5])
  weight = 0.85
  df.append({'Intersection':intersection,'Weight':weight}, ignore_index=True)
  
  print(df)
  </code></pre>
  <p>Allways I get just following result:</p>
  <p>Empty DataFrame</p>
  <p>Columns: [Interval, Weight]</p>