jupyter报错：NameError: name 'CategoricalDtype' is not defined

机器学习 用jupter 进行训练时报错NameError: name 'down_load' is not defined
但第一次进行训练时并未报错
运行代码：

import torch
from torch import nn,optim
from torch.autograd import Variable
from torch.utils.data import DataLoader
from torchvision import transforms
from torchvision import datasets
import os
if not(os.path.exists("./mnist/")) or not os.listdir("./mnist/"):
    down_load = True

train_dataset = datasets.MNIST(
    root = "./mnist/",
    train = True,
    transform = transforms.ToTensor(),
    download = down_load
)

test_dataset = datasets.MNIST(
    root = "./mnist/",
    train = False,
    transform = transforms.ToTensor(),
    download = down_load
)

运行结果及报错内容

尝试过删除重试以及重启jupter 都还是报错

发给我看看运行日志