import xlrd, xlwt
oldbook = xlrd.open_workbook('bar.xlsx')
newbook = xlwt.Workbook()
for sheetname in oldbook.sheet_names():
oldsheet = oldbook.sheet_by_name(sheetname)
newsheet = newbook.add_sheet(sheetname)
for ii in range(oldsheet.nrows):
for jj in range(oldsheet.ncols):
newsheet.write(ii, jj, str(oldsheet.cell_value(ii, jj)).upper())
newbook.save("foo.xlsx")