def cache_num(key, cache=None):
    """Gets the 64bit number from the specified item.

    * http://uwsgi.readthedocs.io/en/latest/Changelog-1.9.9.html#math-for-cache

    :param str|unicode key: The cache key to get value for.

    :param str|unicode cache: Cache name with optional address (if @-syntax is used).

    :rtype: int|long|None
    """
