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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _generate_report_single(self, sid):
        '''Generate report for subfolder given by sid .

        The main purpose of this method is to make sure the subfolder given by
        sid does indeed exist.  All real work is delegated to
        _generate_for_subfolder.

        :param sid: The subfolder id

        Private method.
        '''
        assert self.workbook is not None
        assert sid is not None

        # Ensure subfolder exists
        if not sid in self.folders.subfolders(self.folder_id, self.user):
            subfolder = Folders.id_to_name(sid)
            print("E: subfolder not found: %s" % subfolder, file=sys.stderr)
            return

        self._generate_for_subfolder(sid)