PyTorch实现MNIST数据集手写数字识别详情

import torchvision
import torch
from torch.utils.data import DataLoader
import torch.nn.functional as F

train_data = torchvision.datasets.MNIST(root="./data",train=True,transform=torchvision.transforms.ToTensor(),download=True)
test_data = torchvision.datasets.MNIST(root="./data",train=False,transform=torchvision.transforms.ToTensor(),download=True)

train_loader = DataLoader(train_data,batch_size=32,shuffle=True)
test_loader = DataLoader(test_data,batch_size=32,shuffle=False)

class Net(torch.nn.Module):
    def __init__(self):
        super(Net,self).__init__()
        self.con1 = torch.nn.Conv2d(1,10,kernel_size=5)
        self.con2 = torch.nn.Conv2d(10,20,kernel_size=5)
        self.pooling = torch.nn.MaxPool2d(2)
        self.fc = torch.nn.Linear(320,10)
    def forward(self,x):
        batch_size = x.size(0)
        x = F.relu(self.pooling(self.con1(x)))
        x = F.relu(self.pooling(self.con2(x)))
        x = x.view(batch_size,-1)
        x = self.fc(x)
        return x
#模型实例化        
model = Net()

lossfun = torch.nn.CrossEntropyLoss()
opt = torch.optim.SGD(model.parameters(),lr=0.01,momentum=0.5)

def train(epoch):
    running_loss = 0.0
    for i,(inputs,targets) in enumerate(train_loader,0):
        # inputs,targets = inputs.to(device),targets.to(device)
        opt.zero_grad()
        outputs = model(inputs)
        loss = lossfun(outputs,targets)
        loss.backward()
        opt.step()

        running_loss += loss.item()
        if i % 300 == 299:
            print('[%d，%d] loss:%.3f' % (epoch+1,i+1,running_loss/300))
            running_loss = 0.0

def test():
    total = 0
    correct = 0
    with torch.no_grad():
        for (inputs,targets) in test_loader:
            # inputs, targets = inputs.to(device), targets.to(device)
            outputs = model(inputs)
            _,predicted = torch.max(outputs.data,dim=1)
            total += targets.size(0)
            correct += (predicted == targets).sum().item()
    print(100*correct/total)

if __name__ == '__main__':
    for epoch in range(20):
        train(epoch)
        test()