TypeError: 'generator' object is not subscriptable

Error in chapter 12, which produces the following "TypeError: 'generator' object is not subscriptable" for the code below. 



>>> import openpyxl
>>> wb = openpyxl.load_workbook('example.xlsx')
>>> sheet = wb.active
>>> sheet = wb.active
>>> sheet.columns[1]
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    sheet.columns[1]
TypeError: 'generator' object is not subscriptable
>>> 

RESOLUTION: 
Create a list for the sheet.colums: 
list(sheet.columns)[1] to overcome the generator error - outdated method since python 2 apparently.