Python错误，提示“ AttributeError：无法设置属性”

Question

这是我的代码：

class PermutedMNIST(datasets.MNIST):

    def __init__(self, root="~/.torch/data/mnist", train=True, permute_idx=None):
        super(PermutedMNIST, self).__init__(root, train, download=True)
        assert len(permute_idx) == 28 * 28
        if self.train:
            self.train_data = torch.stack([img.float().view(-1)[permute_idx] / 255
                                           **for img in self.train_data])**
        else:
            self.test_data = torch.stack([img.float().view(-1)[permute_idx] / 255
                                          for img in self.test_data])

    def __getitem__(self, index):

        if self.train:
            img, target = self.train_data[index], self.train_labels[index]
        else:
            img, target = self.test_data[index], self.test_labels[index]

        return img, target

    def get_sample(self, sample_size):
        sample_idx = random.sample(range(len(self)), sample_size)
        return [img for img in self.train_data[sample_idx]]

错误消息：

~./data.py in __init__(self, root, train, permute_idx)
     11 if self.train: 
     12 self.train_data = torch.stack([img.float().view(-1)[permute_idx] / 255 
---> 13 for img in self.train_data]) 
     14 else: 
     15 self.test_data = torch.stack([img.float().view(-1)[permute_idx] / 255
     AttributeError: can't set attribute