class_docstr: A visitor that inspects the graph and looks for dataset keys in use.
code: def visit(self, operation_def, input_values):
      if isinstance(
          operation_def, beam_nodes.ExtractInputForSavedModel
      ):
          self._required_dataset_keys.add(operation_def.dataset_key)
      return nodes.OperationNode(operation_def, input_values).outputs
  
imports: import collections
  import dataclasses
  import hashlib
  from typing import Collection, Dict, Mapping, Optional, Tuple
  from typing import OrderedDict
  import tensorflow
  from tensorflow_transform import analyzer_nodes
  from tensorflow_transform import common_types
  from tensorflow_transform import graph_tools
  from tensorflow_transform import impl_helper
  from tensorflow_transform import nodes
  from tensorflow_transform import tf2_utils
  from tensorflow_transform import tf_utils
  from tensorflow_transform.beam import analyzer_cache
  from tensorflow_transform.beam import beam_nodes
  from tensorflow_transform.beam import combiner_packing_util
label_desc: Use image node_id 2 for calling the _InspectVisitor obj's underlying member method code with example usage: obj.visit(operation_def, input_values) and returns: nodes