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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 folders(self, ann_id=None):
        '''Yields an unordered generator for all available folders.

        By default (with ``ann_id=None``), folders are shown for all
        anonymous users. Optionally, ``ann_id`` can be set to a username,
        which restricts the list to only folders owned by that user.

        :param str ann_id: Username
        :rtype: generator of folder_id
        '''
        ann_id = self._annotator(ann_id)
        if len(self.prefix) > 0:
            prefix = '|'.join([urllib.quote(self.prefix, safe='~'),
                               'topic', ann_id, ''])
        else:
            prefix = '|'.join(['topic', ann_id, ''])
        logger.info('Scanning for folders with prefix %r', prefix)
        return imap(lambda id: self.unwrap_folder_content_id(id)['folder_id'],
                    self.store.scan_prefix_ids(prefix))