new_contents: import pandas as pd
  
  grades_df = pd.DataFrame(
      data={'exam1': [43, 81, 78, 75, 89, 70, 91, 65, 98, 87],
            'exam2': [24, 63, 56, 56, 67, 51, 79, 46, 72, 60]},
      index=['Andre', 'Barry', 'Chris', 'Dan', 'Emilio',
             'Fred', 'Greta', 'Humbert', 'Ivan', 'James']
  )
  
  
  def std_one(col):
      return (col - col.mean()) / col.std()
  
  
  def standardize(df):
      '''
      standardize each column of the DataFrame.
      '''
      return df.apply(std_one)
  
  print standardize(grades_df)
  
subject: Create std_col.py