pytorch实现ResNet50

ResNet50的结构如下：

下面是具体的代码：

import torch
import torch.nn as nn
from torch.nn import functional as F


class ResNet50BasicBlock(nn.Module):
    def __init__(self, in_channel, outs, kernerl_size, stride, padding):
        super(ResNet50BasicBlock, self).__init__()
        self.conv1 = nn.Conv2d(in_channel, outs[0], kernel_size=kernerl_size[0], stride=stride[0], padding=padding[0])
        self.bn1 = nn.BatchNorm2d(outs[0])
        self.conv2 = nn.Conv2d(outs[0], outs[1], kernel_size=kernerl_size[1], stride=stride[0], padding=padding[1])
        self.bn2 = nn.BatchNorm2d(outs[1])
        self.conv3 = nn.Conv2d(outs[1], outs[2], kernel_size=kernerl_size[2], stride=stride[0], padding=padding[2])
        self.bn3 = nn.BatchNorm2d(outs[2])

    def forward(self, x):
        out = self.conv1(x)
        out = F.relu(self.bn1(out))

        out = self.conv2(out)
        out = F.relu(self.bn2(out))

        out = self.conv3(out)
        out = self.bn3(out)

        return F.relu(out + x)


class ResNet50DownBlock(nn.Module):
    def __init__(self, in_channel, outs, kernel_size, stride, padding):
        super(ResNet50DownBlock, self).__init__()
        # out1, out2, out3 = outs
        # print(outs)
        self.conv1 = nn.Conv2d(in_channel, outs[0], kernel_size=kernel_size[0], stride=stride[0], padding=padding[0])
        self.bn1 = nn.BatchNorm2d(outs[0])
        self.conv2 = nn.Conv2d(outs[0], outs[1], kernel_size=kernel_size[1], stride=stride[1], padding=padding[1])
        self.bn2 = nn.BatchNorm2d(outs[1])
        self.conv3 = nn.Conv2d(outs[1], outs[2], kernel_size=kernel_size[2], stride=stride[2], padding=padding[2])
        self.bn3 = nn.BatchNorm2d(outs[2])

        self.extra = nn.Sequential(
            nn.Conv2d(in_channel, outs[2], kernel_size=1, stride=stride[3], padding=0),
            nn.BatchNorm2d(outs[2])
        )

    def forward(self, x):
        x_shortcut = self.extra(x)
        out = self.conv1(x)
        out = self.bn1(out)
        out = F.relu(out)

        out = self.conv2(out)
        out = self.bn2(out)
        out = F.relu(out)

        out = self.conv3(out)
        out = self.bn3(out)
        return F.relu(x_shortcut + out)


class ResNet50(nn.Module):
    def __init__(self):
        super(ResNet50, self).__init__()
        self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3)
        self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)

        self.layer1 = nn.Sequential(
            ResNet50DownBlock(64, outs=[64, 64, 256], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1], padding=[0, 1, 0]),
            ResNet50BasicBlock(256, outs=[64, 64, 256], kernerl_size=[1, 3, 1], stride=[1, 1, 1, 1], padding=[0, 1, 0]),
            ResNet50BasicBlock(256, outs=[64, 64, 256], kernerl_size=[1, 3, 1], stride=[1, 1, 1, 1], padding=[0, 1, 0]),
        )

        self.layer2 = nn.Sequential(
            ResNet50DownBlock(256, outs=[128, 128, 512], kernel_size=[1, 3, 1], stride=[1, 2, 1, 2], padding=[0, 1, 0]),
            ResNet50BasicBlock(512, outs=[128, 128, 512], kernerl_size=[1, 3, 1], stride=[1, 1, 1, 1], padding=[0, 1, 0]),
            ResNet50BasicBlock(512, outs=[128, 128, 512], kernerl_size=[1, 3, 1], stride=[1, 1, 1, 1], padding=[0, 1, 0]),
            ResNet50DownBlock(512, outs=[128, 128, 512], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1], padding=[0, 1, 0])
        )

        self.layer3 = nn.Sequential(
            ResNet50DownBlock(512, outs=[256, 256, 1024], kernel_size=[1, 3, 1], stride=[1, 2, 1, 2], padding=[0, 1, 0]),
            ResNet50BasicBlock(1024, outs=[256, 256, 1024], kernerl_size=[1, 3, 1], stride=[1, 1, 1, 1],
                               padding=[0, 1, 0]),
            ResNet50BasicBlock(1024, outs=[256, 256, 1024], kernerl_size=[1, 3, 1], stride=[1, 1, 1, 1],
                               padding=[0, 1, 0]),
            ResNet50DownBlock(1024, outs=[256, 256, 1024], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1],
                              padding=[0, 1, 0]),
            ResNet50DownBlock(1024, outs=[256, 256, 1024], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1],
                              padding=[0, 1, 0]),
            ResNet50DownBlock(1024, outs=[256, 256, 1024], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1],
                              padding=[0, 1, 0])
        )

        self.layer4 = nn.Sequential(
            ResNet50DownBlock(1024, outs=[512, 512, 2048], kernel_size=[1, 3, 1], stride=[1, 2, 1, 2],
                              padding=[0, 1, 0]),
            ResNet50DownBlock(2048, outs=[512, 512, 2048], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1],
                              padding=[0, 1, 0]),
            ResNet50DownBlock(2048, outs=[512, 512, 2048], kernel_size=[1, 3, 1], stride=[1, 1, 1, 1],
                              padding=[0, 1, 0])
        )

        self.avgpool = nn.AdaptiveAvgPool2d(output_size=(1, 1))

        self.fc = nn.Linear(2048, 10)

    def forward(self, x):
        out = self.conv1(x)
        out = self.maxpool(out)
        out = self.layer1(out)
        out = self.layer2(out)
        out = self.layer3(out)
        out = self.layer4(out)
        out = self.avgpool(out)
        out = out.reshape(x.shape[0], -1)
        out = self.fc(out)
        return out


if __name__ == '__main__':
    x = torch.randn(2, 3, 224, 224)
    net = ResNet50()
    out = net(x)
    print('out.shape: ', out.shape)
    print(out)

和

import torch
from torch import nn, optim
import torchvision.transforms as transforms
from torchvision import datasets
from torch.utils.data import DataLoader
from resnet50 import ResNet50


#  用CIFAR-10 数据集进行实验

def main():
    batchsz = 128

    cifar_train = datasets.CIFAR10('cifar', True, transform=transforms.Compose([
        transforms.Resize((32, 32)),
        transforms.ToTensor(),
        transforms.Normalize(mean=[0.485, 0.456, 0.406],
                             std=[0.229, 0.224, 0.225])
    ]), download=True)
    cifar_train = DataLoader(cifar_train, batch_size=batchsz, shuffle=True)

    cifar_test = datasets.CIFAR10('cifar', False, transform=transforms.Compose([
        transforms.Resize((32, 32)),
        transforms.ToTensor(),
        transforms.Normalize(mean=[0.485, 0.456, 0.406],
                             std=[0.229, 0.224, 0.225])
    ]), download=True)
    cifar_test = DataLoader(cifar_test, batch_size=batchsz, shuffle=True)

    x, label = iter(cifar_train).next()
    print('x:', x.shape, 'label:', label.shape)

    device = torch.device('cuda')
    # model = Lenet5().to(device)
    model = ResNet50().to(device)

    criteon = nn.CrossEntropyLoss().to(device)
    optimizer = optim.Adam(model.parameters(), lr=1e-3)
    # print(model)

    for epoch in range(1000):

        model.train()
        for batchidx, (x, label) in enumerate(cifar_train):
            # [b, 3, 32, 32]
            # [b]
            x, label = x.to(device), label.to(device)

            logits = model(x)
            # logits: [b, 10]
            # label:  [b]
            # loss: tensor scalar
            loss = criteon(logits, label)

            # backprop
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

        print(epoch, 'loss:', loss.item())

        model.eval()
        with torch.no_grad():
            # test
            total_correct = 0
            total_num = 0
            for x, label in cifar_test:
                # [b, 3, 32, 32]
                # [b]
                x, label = x.to(device), label.to(device)

                # [b, 10]
                logits = model(x)
                # [b]
                pred = logits.argmax(dim=1)
                # [b] vs [b] => scalar tensor
                correct = torch.eq(pred, label).float().sum().item()
                total_correct += correct
                total_num += x.size(0)
                # print(correct)

            acc = total_correct / total_num
            print(epoch, 'test acc:', acc)


if __name__ == '__main__':
    main()