code: def _CTCLossGradImpl(op, grad_loss, _):
      # Outputs are: loss, grad
      #
      # Currently there is no way to take the second derivative of this op
      # due to the fused implementation's interaction with tf.gradients(),
      # so we make sure we prevent silently incorrect results by raising
      # an error if the second derivative is requested via prevent_gradient.
      grad_without_gradient = array_ops.prevent_gradient(
          op.outputs[1],
          message="Currently there is no way to take the second "
          " derivative of ctc_loss due to the fused implementation's interaction "
          " with tf.gradients()",
      )
      # Return gradient for inputs and None for
      # labels_indices, labels_values and sequence_length
      return [
          _BroadcastMul(grad_loss, grad_without_gradient),
          None,
          None,
          None,
      ]
  
imports: import uuid
  from tensorflow.python.eager import context
  from tensorflow.python.eager import def_function
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import device
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import function
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import sparse_tensor
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import array_ops_stack
  from tensorflow.python.ops import custom_gradient
  from tensorflow.python.ops import functional_ops
  from tensorflow.python.ops import gen_array_ops
  from tensorflow.python.ops import gen_ctc_ops
  from tensorflow.python.ops import inplace_ops
  from tensorflow.python.ops import linalg_ops
  from tensorflow.python.ops import map_fn
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import nn_ops
  from tensorflow.python.ops import sparse_ops
  from tensorflow.python.ops.nn_grad import _BroadcastMul
  from tensorflow.python.util import deprecation
  from tensorflow.python.util import dispatch
  from tensorflow.python.util import nest
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 5 for calling a global function with example usage: _CTCLossGradImpl(op, grad_loss, _) and returns: list