def METHOD_NAME(self, policy):
    for key, attrs in policy.items():
        self[key].extend(attrs)
        # The keyword 'none' must be the only source expression in the
        # directive value, otherwise it is ignored. If there's more than
        # one directive set, attempt to remove 'none' if it is present
        if NONE in self[key] and len(self[key]) > 1:
            self[key].remove(NONE)