def retrieve(self, tagname, monthyear):
query = Tag.query(Tag.monthyear == monthyear, ancestor=Tag.get_tag_parent_key(tagname))
tagmodels = query.fetch(1)
if len(tagmodels) == 0:
tag = Tag(parent=Tag.get_tag_parent_key(tagname))
tag.name = tagname
tag.monthyear = monthyear
else:
tag = tagmodels[0]
return tag
