@classmethod
def run_once(cls):
    """Call each callback for this class in sequence."""
    if cls.reddit is None:
        raise ValueError(
            'PRAW Reddit session is not set. Run set_reddit first.')
    items = list(cls.seen_filter(cls.items()))
    for func in cls.wrapped_funcs.get(cls.__name__, []):
        for item in items:
            cls.process_return(func(item))
