'Get a release by tag name.
release_from_tag() returns a release with specified tag
while release() returns a release with specified release id
:param str tag_name: (required) name of tag
:returns: :class:`Release <github3.repos.release.Release>`'

def release_from_tag(self, tag_name):

    url = self._build_url(u'releases', u'tags', tag_name, base_url=self._api)
    json = self._json(self._get(url), 200)
    return self._instance_or_null(Release, json)
