Extracting features from a pretrained model using hook function
I want to extract features from some of the layers from a pretrained model. For this aim, I am using thi pretrained model from here. I removed some of the final layers and for loading the pretrained weights, I use strict=False.
The architecture of the model is as follows:
Net(
  (blocks): ModuleList(
    (0): ResNetBasicStem(
      (conv): Conv3d(3, 64, kernel_size=(1, 7, 7), stride=(1, 2, 2), padding=(0, 3, 3), bias=False)
      (norm): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      (activation): ReLU()
    )
    (1): ResStage(
      (res_blocks): ModuleList(
        (0): ResBlock(
          (branch1_conv): Conv3d(64, 256, kernel_size=(1, 1, 1), stride=(1, 2, 2), bias=False)
          (branch1_norm): BatchNorm3d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(64, 64, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(64, 64, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(64, 64, kernel_size=(1, 3, 3), stride=(1, 2, 2), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(64, 256, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
        (1): ResBlock(
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(256, 64, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(64, 64, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(64, 64, kernel_size=(1, 3, 3), stride=(1, 1, 1), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(64, 256, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
        (2): ResBlock(
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(256, 64, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(64, 64, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(64, 64, kernel_size=(1, 3, 3), stride=(1, 1, 1), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(64, 256, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
      )
    )
    (2): ResStage(
      (res_blocks): ModuleList(
        (0): ResBlock(
          (branch1_conv): Conv3d(256, 512, kernel_size=(1, 1, 1), stride=(1, 2, 2), bias=False)
          (branch1_norm): BatchNorm3d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(256, 128, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(128, 128, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(128, 128, kernel_size=(1, 3, 3), stride=(1, 2, 2), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(128, 512, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
        (1): ResBlock(
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(512, 128, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(128, 128, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(128, 128, kernel_size=(1, 3, 3), stride=(1, 1, 1), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(128, 512, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
        (2): ResBlock(
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(512, 128, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(128, 128, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(128, 128, kernel_size=(1, 3, 3), stride=(1, 1, 1), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(128, 512, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
        (3): ResBlock(
          (branch2): BottleneckBlock(
            (conv_a): Conv3d(512, 128, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_a): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_a): ReLU()
            (conv_b): Conv2plus1d(
              (conv_t): Conv3d(128, 128, kernel_size=(3, 1, 1), stride=(1, 1, 1), padding=(1, 0, 0), bias=False)
              (norm): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
              (activation): ReLU()
              (conv_xy): Conv3d(128, 128, kernel_size=(1, 3, 3), stride=(1, 1, 1), padding=(0, 1, 1), bias=False)
            )
            (norm_b): BatchNorm3d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
            (act_b): ReLU()
            (conv_c): Conv3d(128, 512, kernel_size=(1, 1, 1), stride=(1, 1, 1), bias=False)
            (norm_c): BatchNorm3d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
          )
          (activation): ReLU()
        )
      )
    )
  )
)

I use hook function for extracting features from layers and my method for loading the features from (1): ResStage and (2): ResStage is as follows:
class mymodel(nn.Module):
def __init__(self, pretrained=False):
    super(mymodel, self).__init__()
    
    self.activation = {}
    def get_activation(name):
        def hook(model, input, output):
            self.activation[name] = output.detach()
        return hook

    self.r2plus1d = create_r2plus1d()

    self.r2plus1d.Net.blocks[1].register_forward_hook(get_activation('ResBlock1'))
    self.r2plus1d.Net.blocks[2].register_forward_hook(get_activation('ResBlock2'))

def forward(self, x, out_consp = False):
    x = self.r2plus1d(x)
    
    
    block1_output = self.activation['ResBlock1']   # channel_num:256
    block2_output = self.activation['ResBlock2']   # channel_num:512
    
    return block1_output, block2_output

Unfortunately the error says that there is not Net insised the state_dict of the model (when it comes to use from hook function). For other pretrained models I could use such scenarios for extracting features from intermediate layers but seemingly, if I'm not mistaken, I think maybe it would be tricky to extract features from Net.

Looking at the link you provided, the function create_r2plus1d() returns the following
 return Net(blocks=nn.ModuleList(blocks))

Your object self.r2plus1d is already a Net instance, so your line
self.r2plus1d.Net.blocks[1].register_forward_hook(get_activation('ResBlock1'))

is basically like calling Net twice.
You probably only have to call it like that and it should work.
self.r2plus1d.blocks[1].register_forward_hook(get_activation('ResBlock1'))

Let me know if this helps.
