def __init__(self, perturbation: Callable | list[Callable]) -> None:
        """
        Initialize a backdoor poisoning attack.

        :param perturbation: A single perturbation function or list of perturbation functions that modify input.
        """
        super().__init__()
        self.perturbation = perturbation
        self._check_params()

        Initialize a backdoor poisoning attack.

        :param perturbation: A single perturbation function or list of perturbation functions that modify input.
        
art/attacks/poisoning/backdoor_attack.py