As I got output total hours and week number reading from one excel sheet,now I should search that week number in another existing excel sheet and filling that total hours in respective week number column in another existing excel sheet, I should read and write into that existing sheet using xlrd
You can write to Excel worksheets using xlwt (in which case I suppose you have to copy over all the data from the existing sheet manually) or openpyxl (more high-level API, but works only with Excel 2010+). See: Python Excel.