text: 
  
  from pandas import DataFrame
  # state abbreviations
  
  def add_state_names(new_df):
      # TODO add a column of corresponding state names
      # dict with abbreviations and state names
      # create a new column that is a copy of the first but mapped with the names 
      # concat with axis=1
  
      # create a copy so it doesn't mess with the original
      my_df = new_df.copy()    
  
      # dictionary of names and abbreviations
      names_map = {'CA': 'California', 'CO': 'Colorado', 'CT': 'Conneticut'}
  
      # new column with names
      my_df['names'] = my_df['abbrev'].map(names_map)
  
      return my_df
  
  
  if __name__ == '__main__':
  
      df = DataFrame({'abbrev': ['CA', 'CO', 'CT', 'DC', 'TX']})
      print(df.head())
  
      df2 = add_state_names(df)
      print(df2.head())
  
      df3 = DataFrame({'a': [1, 2, 3, 4]})
      print(df3.head())
  
  