games.columns = map(str.lower, games.columns)
games['total_sum'] = games['na_sales'] + games['eu_sales'] + games['jp_sales'] + games['other_sales']
games

--------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-78-d2da612ab567> in <module>
----> 1 games.columns = map(str.lower, games.columns)
      2 games
      3 #games['total_sum'] = games['na_sales'] + games['eu_sales'] + games['jp_sales'] + games['other_sales']
      4 #games

AttributeError: 'Index' object has no attribute 'columns'