there is mistake in historical_sales_data.xls
there is a 'error' blank in the column name 'Total'. if I use pandas to handle this file, the result is confusing.
Actually, the column name in the Excel file should be 'Total' without the 'error' blank.
import pandas
df = pandas.read_excel('./historical_sales_data.xls')
print(df['Fish']) # this is ok
print(df['Total']) # error!