object is not subscriptable... Error Message?

[Shafla]

I am trying to access values of cells in an exel workbook. i am following an exercise from a book and getting the following error message;

>>> import openpyxl
>>> wb=openpyxl.load_workbook('Example_Page267.xlsx')
>>> sheet=wb.active
>>> sheet.columns[1]
Traceback (most recent call last):
  File "<pyshell#151>", line 1, in <module>
    sheet.columns[1]
TypeError: 'generator' object is not subscriptable

any idea what i am doing wrong?