class_docstr: Dense Feature Stack Block
  
  - Stack is initialized with the input from above layers.
  - Iteratively the output of convolution layers is added to the feature stack.
  - Each sequential convolution is performed over all the previous stacked
    channels.
  
  Diagram example:
  
      feature_stack = [Input]
      feature_stack = [feature_stack, conv(feature_stack)]
      feature_stack = [feature_stack, conv(feature_stack)]
      feature_stack = [feature_stack, conv(feature_stack)]
      ...
      Output = [feature_stack, conv(feature_stack)]
docstr: :return:  dense feature stack block
docstr_tok: [":","return",":","dense","feature","stack","block"]
code: def create_block(self):
      """
  
      :return:  dense feature stack block
      """
      dfs_block = []
      for _ in self.dilation_rates:
          if self.use_bdo:
              conv = ChannelSparseConvolutionalLayer(
                  self.n_dense_channels,
                  kernel_size=self.kernel_size,
                  **self.kwargs,
              )
          else:
              conv = ConvolutionalLayer(
                  self.n_dense_channels,
                  kernel_size=self.kernel_size,
                  **self.kwargs,
              )
  
          dfs_block.append(conv)
  
      return dfs_block
  
imports: from __future__ import absolute_import, print_function
  import tensorflow
  from niftynet.io.misc_io import image3_axial
  from niftynet.layer import layer_util
  from niftynet.layer.affine_augmentation import AffineAugmentationLayer
  from niftynet.layer.base_layer import TrainableLayer
  from niftynet.layer.bn import BNLayer
  from niftynet.layer.channel_sparse_convolution import ChannelSparseConvolutionalLayer
  from niftynet.layer.convolution import ConvolutionalLayer
  from niftynet.layer.linear_resize import LinearResizeLayer
  from niftynet.layer.downsample import DownSampleLayer
  from niftynet.network.base_net import BaseNet
  from collections import namedtuple
label_desc: Use image node_id 2 for calling the DenseFeatureStackBlock obj's underlying member method code with example usage: obj.create_block() and returns: dfs_block