pytorch练习一MNIST_mnist false下载

深度学习入门的第一个一般都是MNIST,很多框架都是这个，就像编程语言第一个程序是hello world!,单片机第一个程序是点亮一个LED一样。

import os
 
import torch
import torch.nn as nn
from torch.autograd import Variable
import torch.utils.data as Data
import torchvision
import matplotlib.pyplot as plt
 
torch.manual_seed(1)  # reproducible
 
EPOCH = 8
BATCH_SIZE = 50
LR = 0.001
DOWNLOAD_MNIST = False
 
 
# 下载数据集
if not (os.path.exists('./mnist/')) or not os.listdir('./mnist/'):
    DOWNLOAD_MNIST = True
 
train_data = torchvision.datasets.MNIST(
    root='./mnist/',
    train=True,
    # 将一张图片或numpy数组转成(C × H ×W)torch.FloatTensor并归一化[0.0,0.1]
    transform=torchvision.transforms.ToTensor(),
    download=DOWNLOAD_MNIST,
)
 
print(train_data.train_data.size())  # (60000, 28,28)
print(train_data.train_labels.size())  # (60000)
plt.imshow(train_data.train_data[1].numpy(), cmap='gray')  # train_data[0]
plt.title('%i' % train_da