src/model.py

import torch
from torch import nn
from torchvision import transforms
from torchvision.models import resnet18,resnet50,ResNet50_Weights

class SimpleCNN(nn.Module):
    def __init__(self, num_inputs=1,input_size=28,num_classes=10, dropout_rate=0.3):
        super().__init__()

        self.features = nn.Sequential(
            # Block 1
            nn.Conv2d(num_inputs, 32, kernel_size=3, padding=1),
            nn.BatchNorm2d(32),
            nn.ReLU(),
            nn.MaxPool2d(2),

            # Block 2
            nn.Conv2d(32, 64, kernel_size=3, padding=1),
            # 【修复 1】你之前写的是 62，必须是 64 才能匹配上一层的输出
            nn.BatchNorm2d(64), 
            nn.ReLU(),
            nn.MaxPool2d(2),
        )
        final_size = input_size // 4
        flatten_dim = 64 * final_size * final_size

        self.classifier = nn.Sequential(
            nn.Flatten(),
            # 计算逻辑: 28 -> 14 -> 7，通道 64
            nn.Linear(flatten_dim, 512),
            nn.BatchNorm1d(512),
            nn.ReLU(),
            nn.Dropout(dropout_rate),
            nn.Linear(512, num_classes),
        )

        self.apply(self._init_weights)

    def _init_weights(self, m):
        # 【修复 2】你之前写的是 nn.Linaer (拼写错误)，导致全连接层没有被正确初始化！
        if isinstance(m, (nn.Conv2d, nn.Linear)): 
            nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
        
        elif isinstance(m, (nn.BatchNorm2d, nn.BatchNorm1d)):
            nn.init.constant_(m.weight, 1)
            # 【修复 3】你之前写的是 m.weiht (拼写错误)，导致偏置没有归零
            nn.init.constant_(m.bias, 0) 

    # 【修复 4】你之前的代码里完全漏掉了 forward 函数！
    # 没有这个函数，模型根本不知道怎么跑数据，虽然不报错(如果没调用)，但跑起来就是随机的
    def forward(self, x):
        x = self.features(x)
        x = self.classifier(x)
        return x

class ResNet18_CIFAR(nn.Module):
    def __init__(self,num_inputs=3,num_classes=10,dropout_rate=0.0):
        super().__init__()

        self.aug = nn.Sequential(
            transforms.RandomHorizontalFlip(),
            transforms.RandomCrop(32,padding=4,padding_mode='reflect'),
        )

        self.net = resnet18(weights=None)

        self.net.conv1 = nn.Conv2d(num_inputs,64,kernel_size=3,stride=1,padding=1,bias=False)
        self.net.maxpool = nn.Identity()

        self.net.fc = nn.Linear(512,num_classes)

    def forward(self,x):
        if self.training:
            x = self.aug(x)
        return self.net(x)

class TransferResNet50(nn.Module):
    def __init__(self, num_classes=10, dropout_rate=0.0):
        super().__init__()

        print("⬇️ Loading Pre-trained ResNet50 (ImageNet)...")
        # 1. 正确加载权重
        self.net = resnet50(weights=ResNet50_Weights.DEFAULT)

        # 2. 全网微调 (不冻结)
        # 因为 CIFAR-10 和 ImageNet 差异较大 (清晰度、物体类别)，微调 Backbone 是必须的
        # 我们已经在 train.py 里用了极小的 backbone_lr (1e-5) 来保护它，所以这里不需要 freeze
        
        # 3. 替换分类头
        num_ftrs = self.net.fc.in_features
        self.net.fc = nn.Sequential(
            nn.Dropout(dropout_rate),
            nn.Linear(num_ftrs, num_classes),
        )
    
    def forward(self, x):
        return self.net(x)