title: python Pandas dataframe returns nonetype form a function
body: <pre><code>import pandas as pd
  def create_df():
      data = {'state': ['Ohio','Ohio','Ohio','Nevada','Nevada'],
             'year': [2000,2001,2002,2001,2002],
             'pop': [1.5,1.7,3.6,2.4,2.9]}
      df = pd.DataFrame(data)
      return df
  create_df()
  #print(df) 
  #why the  adding print(df) returns nonetype? how can I print this df?
  </code></pre>
  <p><strong>why the  adding print(df) returns nonetype? how can I print this df?</strong></p>