code: def apply_weight_norm(self):
      self.res_block = weight_norm(self.res_block)
      for idx, layer in enumerate(self.main_block):
          if len(layer.state_dict()) != 0:
              self.main_block[idx] = weight_norm(layer)
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  from torch.nn.utils import weight_norm
label_desc: Use image node_id 4 for calling the DBlock obj's underlying member method code with example usage: obj.apply_weight_norm() without return types