models/model_loader.py

import timm
import torch.nn as nn


def replace_last_layer(model, num_classes):
    modules = list(model.named_modules())

    for name, module in reversed(modules):
        if isinstance(module, nn.Linear):
            in_features = module.in_features
            new_fc = nn.Linear(in_features, num_classes)
            new_fc.requires_grad = True
            if "." in name:
                parent_name, child_name = name.rsplit(".", 1)
                parent = dict(model.named_modules())[parent_name]
                setattr(parent, child_name, new_fc)
            else:
                setattr(model, name, new_fc)
            break
        elif isinstance(module, nn.Conv2d):
            out_channels = module.out_channels
            new_fc = nn.Conv2d(
                out_channels,
                num_classes,
                kernel_size=module.kernel_size,
                stride=module.stride,
                padding=module.padding,
            )
            new_fc.requires_grad = True
            if "." in name:
                parent_name, child_name = name.rsplit(".", 1)
                parent = dict(model.named_modules())[parent_name]
                setattr(parent, child_name, new_fc)
            else:
                setattr(model, name, new_fc)
            break


def enable_first_layer_grad(model):
    for name, module in model.named_modules():
        if isinstance(module, nn.Conv2d):
            module.requires_grad = True
            break


def create_model(key, in_chans=1, num_classes=1):
    model = timm.create_model(
        key, pretrained=False, in_chans=in_chans, num_classes=num_classes
    )
    for param in model.parameters():
        param.requires_grad = False
    enable_first_layer_grad(model)
    replace_last_layer(model, num_classes)

    return model