A SpreadsheetsService singleton, used to perform
        operations on the actual spreadsheet.

def sheets_service(self):
        """ A SpreadsheetsService singleton, used to perform
        operations on the actual spreadsheet. """
        if not hasattr(self, '_sheets_service'):
            service = SpreadsheetsService()
            service.email = self.google_user
            service.password = self.google_password
            service.source = SOURCE_NAME
            service.ProgrammaticLogin()
            self._sheets_service = service
        return self._sheets_service