请解释一下import matplotlib.pyplot as plt import numpy as np import torch import torch.utils.data.dataloader as Loader import torchvision import torchvision.transforms as transforms import torch.nn as nn import torch.nn.functional as F import torch.optim as optim from torch.utils.tensorboard import SummaryWriter BATCH SIZE=4 transform - transforms.Compose( [transforms. ToTensor0, transforms.Normalize((0.5,), (0.5.)) trainset=torchvision.datasets.FashionMNIST(' /data', download True, train=True, transform=transform) testset=torchvision.datasets.FashionMNIST(' /data', download=True, train=False, transform=transform) trainloader=Loader.DataLoader(trainset, batch size=BATCH SIZE, shuffle True)testloader=Loader.Datal oader(testset, batch size=BATCH SIZE, shuffle- False)classes s ('T- shirt/top', 'Trouser', 'Pullover', 'Dress', 'Coat', 'Sandal', 'Shirt', 'Sneaker', 'Bag', 'Ankle Boot') class Net(nn.Module);: def_ init (self): super(Net, self). init 0这段代码