from torch import nn


class DigitCNN(nn.Module):
    """用于识别 28×28 灰度手写数字的小型卷积神经网络。"""

    def __init__(self):
        super().__init__()
        self.features = nn.Sequential(
            nn.Conv2d(1, 32, kernel_size=3, padding=1),
            nn.ReLU(),
            nn.MaxPool2d(2),
            nn.Conv2d(32, 64, kernel_size=3, padding=1),
            nn.ReLU(),
            nn.MaxPool2d(2),
        )
        self.classifier = nn.Sequential(
            nn.Flatten(),
            nn.Linear(64 * 7 * 7, 128),
            nn.ReLU(),
            nn.Dropout(0.2),
            nn.Linear(128, 10),
        )

    def forward(self, x):
        x = self.features(x)
        return self.classifier(x)