code: def _graph_def_from_concrete_fn(cfs):
      if len(cfs) != 1:
          raise NotImplementedError(
              "Only a single concrete function is supported."
          )
  
      frozen_fn = _convert_variables_to_constants_v2(
          cfs[0], lower_control_flow=False
      )
      graph_def = frozen_fn.graph.as_graph_def(add_shapes=True)
  
      # run a Grappler's constant folding pass.
      fn_inputs = [
          t for t in frozen_fn.inputs if t.dtype != _dtypes.resource
      ]
      graph_def = _run_graph_optimizations(
          graph_def,
          fn_inputs,
          frozen_fn.outputs,
          config=_get_grappler_config(["constfold", "dependency"]),
          graph=frozen_fn.graph,
      )
      return graph_def
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import logging
  import os.path
  from six import string_types
  from tqdm import tqdm
  import tensorflow
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework.convert_to_constants import convert_variables_to_constants_v2
  from tensorflow.python.framework.function_def_to_graph import function_def_to_graph
  from tensorflow.python.keras.saving import saving_utils
  from tensorflow.lite.python.util import run_graph_optimizations
  from tensorflow.lite.python.util import get_grappler_config
  from .converter import TF2Converter
  from coremltools.converters.mil.frontend.tensorflow.basic_graph_ops import fill_outputs
  from coremltools.converters.mil.frontend.tensorflow.tf_graph_pass import constant_propagation, remove_variable_nodes, tensor_array_resource_removal, insert_get_tuple, delete_disconnected_nodes, fuse_dilation_conv
  from coremltools.converters.mil.frontend.tensorflow2.tf_graph_pass import flatten_sub_graph_namespaces, rewrite_control_flow_functions
  from coremltools.converters.mil.frontend.tensorflow.tfssa import NetworkEnsemble, SSAFunction
  from coremltools.converters.mil.frontend.tensorflow.parsed_tf_node import ParsedTFNode
  from coremltools.converters.mil.frontend.tensorflow.load import TFLoader
label_desc: Use image node_id 8 for calling the TF2Loader obj's underlying member method code with example usage: obj._graph_def_from_concrete_fn(cfs) and returns: graph_def