from datetime import datetime
import xlrd
book = xlrd.open_workbook('test.xls')
sheet = book.sheet_by_index(0)
a1 = sheet.cell_value(rowx=0, colx=0)
print(a1)
print(xlrd.xldate_as_tuple(a1, 1))
a1_tuple = xlrd.xldate_as_tuple(a1, book.datemode)
print(a1_tuple)
a1_datetime = datetime(*a1_tuple)
print(a1_datetime.strftime('%m/%d/%Y'))
xlrd исходное значение ячейки