code: def _get_custom_layers(spec):
      """
  
      Returns a list of all neural network custom layers in the spec.
  
      Parameters
      ----------
      spec: mlmodel spec
  
      Returns
      -------
  
      [NN layer] A list of custom layer implementations
      """
      layers = _get_nn_layers(spec)
      layers_out = []
      for layer in layers:
          if layer.WhichOneof("layer") == "custom":
              layers_out.append(layer)
  
      return layers_out
  
imports: import math
  import numpy
  import os
  import six
  import warnings
  import sys
  from coremltools.proto import Model_pb2
  from coremltools.models._deprecation import deprecated
  from .._deps import _HAS_SKLEARN
label_desc: Use image node_id 22 for calling a global function with example usage: _get_custom_layers(spec) and returns: layers_out