models.py

import torch
import torch.nn as nn
from torchvision import models


class Stem(nn.Module):
    def __init__(self):
        super(Stem, self).__init__()
        self.conv = nn.Sequential(
            nn.Conv2d(3, 64, kernel_size=7, stride=2),
            nn.MaxPool2d(kernel_size=3, stride=2),
        )

    def forward(self, x):
        x = self.conv(x)
        return x


class ResidualBlock(nn.Module):
    def __init__(self, in_channels, out_channels, stride=1):
        super(ResidualBlock, self).__init__()
        self.conv1 = nn.Sequential(
            nn.Conv2d(in_channels, out_channels // 4, stride=1, kernel_size=1),
            nn.BatchNorm2d(out_channels // 4),
            nn.ReLU(inplace=True),
        )
        self.conv2 = nn.Sequential(
            nn.Conv2d(
                out_channels // 4,
                out_channels // 4,
                stride=stride,
                kernel_size=3,
                padding=1,
            ),
            nn.BatchNorm2d(out_channels // 4),
            nn.ReLU(inplace=True),
        )

        self.conv3 = nn.Sequential(
            nn.Conv2d(out_channels // 4, out_channels, kernel_size=1, stride=1),
            nn.BatchNorm2d(out_channels),
        )

        self.shortcut = (
            nn.Identity()
            if in_channels == out_channels
            else nn.Sequential(
                nn.Conv2d(in_channels, out_channels, kernel_size=1, stride=stride),
                nn.BatchNorm2d(out_channels),
            )
        )

        self.relu = nn.ReLU(inplace=True)

    def forward(self, x):
        identity = self.shortcut(x)
        x = self.conv1(x)
        x = self.conv2(x)
        x = self.conv3(x)
        x += identity
        x = self.relu(x)
        return x


def make_layer(in_channels, out_channels, block, num_blocks):
    layers = []
    for i in range(num_blocks):
        layers.append(block(in_channels, out_channels))
        in_channels = out_channels

    return layers


class FromZero(nn.Module):
    def __init__(self, num_classes=10):
        super(FromZero, self).__init__()
        self.stem = Stem()
        self.layer1 = nn.Sequential(*make_layer(64, 64, ResidualBlock, 2))
        self.layer2 = nn.Sequential(
            ResidualBlock(64, 128, stride=2), ResidualBlock(128, 128)
        )
        self.layer3 = nn.Sequential(
            ResidualBlock(128, 256, stride=2), ResidualBlock(256, 256)
        )
        self.layer4 = nn.Sequential(
            ResidualBlock(256, 512, stride=2), ResidualBlock(512, 512)
        )

        self.flatten = nn.Flatten()
        self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
        self.fc = nn.Linear(512, num_classes)

    def forward(self, x):
        x = self.stem(x)
        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.layer4(x)
        x = self.avgpool(x)
        x = self.flatten(x)
        x = self.fc(x)
        return x


class PreTrained(nn.Module):
    def __init__(self, num_classes):
        super().__init__()
        self.model = models.resnet18(
            weights=models.ResNet18_Weights.IMAGENET1K_V1, progress=True
        )
        for param in self.model.parameters():
            param.requires_grad = False

        self.model.fc = nn.Sequential(
            nn.Linear(self.model.fc.in_features, 512),
            nn.ReLU(inplace=True),
            nn.Linear(512, num_classes),
        )

    def forward(self, x):
        return self.model(x)