I would like to access worksheets of a spreadsheet. I've copied the main workbook to another workbook using xlutils.copy(). But don't know the right way to access worksheets using xlwt module. 
My sample code:

```
import xlrd
import xlwt
from xlutils.copy import copy

wb1 = xlrd.open_workbook('workbook1.xls', formatting_info=True)
wb2 = copy(master_wb)

worksheet_name = 'XYZ' (worksheet_name is a iterative parameter)

worksheet = wb2.get_sheet(worksheet_name)

```

Could someone please tell me what's the right command line to access the existing worksheets in a workbook using xlwt module? I know we can use 'add\_sheet' method to add a worksheet in the existing workbook using xlwt module.

Any help, appreciated.