docs: def __writeData(self, targetPath, fields, rows):
          ''' write data '''
          if path.exists(targetPath):
              LOG.error("Target file exists: %s" % path.abspath(targetPath) )
              raise UfException(Errors.FILE_EXIST, "can't write to a existing file") #because xlwt doesn't support it
  
          with ExcelLib(fileName = targetPath, mode = ExcelLib.WRITE_MODE) as excel:
              excel.writeRow(0, fields)
              for index, row in enumerate(rows):
                  excel.writeRow(index+1, row)