I would like to fine-tune by adding layers to the resnet50 pre-trained model.
here’s resnet50 imported
from torchvision import models

resnet50 = models.resnet50(pretrained = True)
resnet50.fc = nn.Identity()

sample = torch.randn(1, 3, 224, 224)
resnet50(sample).size()


torch.Size([1, 2048])

Here are the layers to add.
class net(nn.Module):
    def __init__(self):
        super(net, self).__init__()
        self.fc = nn.Linear(2048, 128)
        
        self.branch_a1 = nn.Linear(128, 32)
        self.branch_a2 = nn.Linear(32, 1)
        
        self.branch_b1 = nn.Linear(128, 5)
    
    def forward(self, x):
        x = F.leaky_relu(self.fc(x))
        
        # branch a
        a = F.leaky_relu(self.branch_a1(x))
        out1 = self.branch_a2(a)
        
        # branch b
        out2 = self.branch_b1(x)
        
        return out1, out2

And I tie the two models together with nn.sequential.
model = nn.Sequential(resnet50, net)
model

I thought it would work, but I get an error. What should I do?
 ---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-55-cdc7b18bb3fc> in <module>
----> 1 model = nn.Sequential(resnet50, net)
      2 model

c:\users\kimsunghun\anaconda3\envs\pytorch\lib\site-packages\torch\nn\modules\container.py in __init__(self, *args)
     52         else:
     53             for idx, module in enumerate(args):
---> 54                 self.add_module(str(idx), module)
     55 
     56     def _get_item_by_idx(self, iterator, idx):

c:\users\kimsunghun\anaconda3\envs\pytorch\lib\site-packages\torch\nn\modules\module.py in add_module(self, name, module)
    187         if not isinstance(module, Module) and module is not None:
    188             raise TypeError("{} is not a Module subclass".format(
--> 189                 torch.typename(module)))
    190         elif not isinstance(name, torch._six.string_classes):
    191             raise TypeError("module name should be a string. Got {}".format(

TypeError: __main__.net is not a Module subclass