def __init__(self, key: np.ndarray, value=None):
        """
        Create an instance of a key/value to pair to be used in a `SortedList`.

        :param key: The sample to be matched against.
        :param value: The mapped value.
        """
        self.key = key
        self.value = value

        Create an instance of a key/value to pair to be used in a `SortedList`.

        :param key: The sample to be matched against.
        :param value: The mapped value.
        
art/estimators/regression/blackbox.py