title: Pandas dataframe add values in a loop
body: <p>I am trying to append dynamically to a dataframe a single value that i am generating in a loop.</p>
  
  <pre><code>global results_df
  results_df=pd.DataFrame()
  
  avg =109
  
  std_dev = 12
  
  # Loop through many simulations
  for i in range(1000):    
      # Choose random inputs 
      rev_sim = np.random.normal(avg, std_dev, 1).round(0)#Rounding to 0 decimals
  
      # Build the dataframe based on the inputs
      df_res = pd.DataFrame(data={'REV_SIM': rev_sim})
      results_df.append(df_res)
  </code></pre>
  
  <p>But my results_df is empty.</p>