src/model.py

import torch
import torch.nn as nn


# define the CNN architecture
# MY CODE HERE

class ResidualBlock(nn.Module):
    def __init__(self, in_ch, out_ch, stride=1):
        super().__init__()
        self.conv1 = nn.Conv2d(in_ch, out_ch, 3, stride, 1, bias=False)
        self.bn1   = nn.BatchNorm2d(out_ch)
        self.relu  = nn.ReLU(True)
        self.conv2 = nn.Conv2d(out_ch, out_ch, 3, 1, 1, bias=False)
        self.bn2   = nn.BatchNorm2d(out_ch)
        self.shortcut = nn.Identity()
        if stride != 1 or in_ch != out_ch:
            self.shortcut = nn.Sequential(
                nn.Conv2d(in_ch, out_ch, 1, stride, bias=False),
                nn.BatchNorm2d(out_ch)
            )
    def forward(self, x):
        out = self.relu(self.bn1(self.conv1(x)))
        out = self.bn2(self.conv2(out))
        out += self.shortcut(x)
        return self.relu(out)
            
class MyModel(nn.Module):
    def __init__(self, num_classes: int = 1000, dropout: float = 0.7) -> None:
            super().__init__()
            self.Backbone = nn.Sequential(
                ResidualBlock(3, 64, 1),
                ResidualBlock(64, 128, 2),
                ResidualBlock(128, 256, 2),
                ResidualBlock(256, 512, 2),
                nn.AdaptiveAvgPool2d((1,1))
            )
            self.Classifier = nn.Sequential(
                nn.Flatten(),
                nn.Linear(512, 512),
                nn.BatchNorm1d(512),
                nn.ReLU(True),
                nn.Dropout(dropout),
                
                nn.Linear(512,192),
                nn.BatchNorm1d(192),
                nn.ReLU(True),
                nn.Dropout(dropout),
                
                nn.Linear(192, num_classes)
            )
            
    def forward(self, x):
        return self.Classifier(self.Backbone(x))
            


######################################################################################
#                                     TESTS
######################################################################################
import pytest


@pytest.fixture(scope="session")
def data_loaders():
    from .data import get_data_loaders

    return get_data_loaders(batch_size=2)


def test_model_construction(data_loaders):

    model = MyModel(num_classes=23, dropout=0.3)

    dataiter = iter(data_loaders["train"])
    images, labels = next(dataiter)

    out = model(images)

    assert isinstance(
        out, torch.Tensor
    ), "The output of the .forward method should be a Tensor of size ([batch_size], [n_classes])"

    assert out.shape == torch.Size(
        [2, 23]
    ), f"Expected an output tensor of size (2, 23), got {out.shape}"