code: def tag(self, sha):
          
          json = None
          if sha:
              url = self._build_url('git', 'tags', sha, base_url=self._api)
              json = self._json(self._get(url), 200)
          return Tag(json) if json else None
docs: Get an annotated tag.
  
          http://learn.github.com/p/tagging.html
  
          :param str sha: (required), sha of the object for this tag
          :returns: :class:`Tag <github3.git.Tag>`