docs: def _get_tags_by_num(self):
  		"""
  		Return a dictionary mapping revision number to tags for that number.
  		"""
  		by_revision = operator.attrgetter('revision')
  		tags = sorted(self.get_tags(), key=by_revision)
  		revision_tags = itertools.groupby(tags, key=by_revision)
  
  		def get_id(rev):
  			return rev.split(':', 1)[0]
  		return dict(
  			(get_id(rev), [tr.tag for tr in tr_list])
  			for rev, tr_list in revision_tags
  		)