Perform the L_2 attack on the given instance for the given targets.

    If self.targeted is true, then the targets represents the target labels
    If self.targeted is false, then targets are the original class labels

def attack(self, imgs, targets):
    """
    Perform the L_2 attack on the given instance for the given targets.

    If self.targeted is true, then the targets represents the target labels
    If self.targeted is false, then targets are the original class labels
    """

    r = []
    for i in range(0, len(imgs), self.batch_size):
      _logger.debug(
          ("Running CWL2 attack on instance %s of %s", i, len(imgs)))
      r.extend(
          self.attack_batch(imgs[i:i + self.batch_size],
                            targets[i:i + self.batch_size]))
    return np.array(r)