code: def _dflt_unit_sizes(num_blocks):
      """Returns a default set of values for the unit sizes."""
      ret = []
      unit_size = 64
      for _ in range(num_blocks):
          ret.append(unit_size)
          unit_size = min(unit_size * 2, 512)
      return ret
  
imports: import numpy
  from scipy.sparse import dok_matrix
  from .neural_network import ConvNeuralNetwork, MultiLayerPerceptron, get_cnn_layer_labels, get_mlp_layer_labels, is_a_conv_layer_label
  from .nn_modifiers import NNModifier
  from ..utils.general_utils import get_dok_mat_with_set_coords
label_desc: Use image node_id 6 for calling a global function with example usage: _dflt_unit_sizes(num_blocks) and returns: ret