model.py

import torch
from torch import nn

class ALexNet(nn.Module):
  def __init__(self, input_shape: int, hidden_units: int, output_shape):
    super().__init__()
    self.block1 = nn.Sequential(
    nn.Conv2d(input_shape, 64, kernel_size=3, padding=1),
    nn.BatchNorm2d(64),
    nn.ReLU(),
    nn.MaxPool2d(2, 2)
    )
    self.block2 = nn.Sequential(
        nn.Conv2d(64, 192, kernel_size=3, padding=1),
        nn.BatchNorm2d(192),
        nn.ReLU(),
        nn.MaxPool2d(2, 2)
    )
    self.block3 = nn.Sequential(
        nn.Conv2d(192, 384, kernel_size=3, padding=1),
        nn.BatchNorm2d(384),
        nn.ReLU()
    )
    self.block4 = nn.Sequential(
        nn.Conv2d(384, 256, kernel_size=3, padding=1),
        nn.BatchNorm2d(256),
        nn.ReLU()
    )
    self.block5 = nn.Sequential(
        nn.Conv2d(256, 256, kernel_size=3, padding=1),
        nn.BatchNorm2d(256),
        nn.ReLU(),
        nn.MaxPool2d(2, 2)
    )

    with torch.no_grad():
      dummy = torch.zeros(1, input_shape, 32, 32)  # change 224 if needed
      x = self.block1(dummy)
      x = self.block2(x)
      x = self.block3(x)
      x = self.block4(x)
      x = self.block5(x)
      self.flattened_size = x.view(1, -1).shape[1]
    self.flatten = nn.Flatten()
    self.fc1 = nn.Sequential(
        nn.Linear(in_features=self.flattened_size,
                  out_features=1024),
        nn.ReLU(),
        nn.Dropout(0.5)
    )
    self.fc2 = nn.Sequential(
        nn.Linear(1024, 1024),
        nn.ReLU(),
        nn.Dropout(0.5)
    )
    self.classifier = nn.Sequential(
        nn.Linear(1024, output_shape)
    )

  def forward(self, x: torch.Tensor):
    x = self.block1(x)
    x = self.block2(x)
    x = self.block3(x)
    x = self.block4(x)
    x = self.block5(x)
    x = self.flatten(x)
    x = self.fc1(x)
    x = self.fc2(x)
    x = self.classifier(x)

    return x