When I Import xlwt directly just Example , 

try:
 import xlwt
 from xlwt import Borders
except ImportError:
 xlwt = None

then working fine with

workbook = xlwt.Workbook()

But when I used the python lib for xlwt :~ https://pypi.org/project/xlwt/#files and put into custom like this

from odoo.addons.inventory.python_lib import xlwt

and calling the

workbook = xlwt.Workbook()

That time error popup
AttributeError: 'NoneType' object has no attribute 'Workbook'