def parse_cache_control_header(value, on_update=None, cls=None):
    if cls is None:
        cls = RequestCacheControl
    if not value:
        return cls(None, on_update)
    return cls(parse_dict_header(value), on_update)
Parse a cache control header.  The RFC differs between response and
dataset/ETHPy150Open Eforcers/gae-flask-todo/lib/werkzeug/http.py/parse_cache_control_header