def last_version():
    """
        Fetch the last version from pypi and return it. On successful fetch from pypi, the response
        is cached 24h, on error, it is cached 10 min.

        :return: the last django-cas-server version
        :rtype: unicode
    """
    try:
        last_update, version, success = last_version._cache
    except AttributeError:
        last_update = 0
        version = None
        success = False
    cache_delta = 24 * 3600 if success else 600
    if (time.time() - last_update) < cache_delta:
        return version
    else:
        try:
            req = requests.get(settings.CAS_NEW_VERSION_JSON_URL)
            data = json.loads(req.text)
            version = data["info"]["version"]
            last_version._cache = (time.time(), version, True)
            return version
        except (
            KeyError,
            ValueError,
            requests.exceptions.RequestException
        ) as error:  # pragma: no cover (should not happen unless pypi is not available)
            logger.error(
                "Unable to fetch %s: %s" % (settings.CAS_NEW_VERSION_JSON_URL, error)
            )
            last_version._cache = (time.time(), version, False)
Fetch the last version from pypi and return it. On successful fetch from pypi, the response
        is cached 24h, on error, it is cached 10 min.

        :return: the last django-cas-server version
        :rtype: unicode