class_docstr: Combine function that computes metric using initial state from extracts.
code: def add_input(self, accumulator: Any, element: types.Extracts):
      def get_combiner_input(element, i):
          item = element[_COMBINER_INPUTS_KEY][i]
          if item is None:
              item = element[_DEFAULT_COMBINER_INPUT_KEY]
          return item
  
      results = []
      for i, (c, a) in enumerate(zip(self._combiners, accumulator)):
          try:
              combiner_input = get_combiner_input(element, i)
              result = c.add_inputs(a, combiner_input)
          except Exception as e:
              raise RuntimeError(
                  f'add_input failed on "{c}" with inputs:\n{combiner_input}'
              ) from e
          results.append(result)
      return tuple(results)
  
imports: import copy
  import datetime
  import itertools
  import numbers
  from typing import Any, Dict, Iterable, Iterator, List, NamedTuple, Optional, Tuple, Type, TypeVar, Union
  import apache_beam
  import numpy
  from tensorflow_model_analysis import constants
  from tensorflow_model_analysis.api import types
  from tensorflow_model_analysis.evaluators import counter_util
  from tensorflow_model_analysis.evaluators import eval_saved_model_util
  from tensorflow_model_analysis.evaluators import evaluator
  from tensorflow_model_analysis.evaluators import jackknife
  from tensorflow_model_analysis.evaluators import keras_util
  from tensorflow_model_analysis.evaluators import metrics_validator
  from tensorflow_model_analysis.evaluators import poisson_bootstrap
  from tensorflow_model_analysis.extractors import slice_key_extractor
  from tensorflow_model_analysis.metrics import metric_specs
  from tensorflow_model_analysis.metrics import metric_types
  from tensorflow_model_analysis.metrics import metric_util
  from tensorflow_model_analysis.proto import config_pb2
  from tensorflow_model_analysis.slicer import slicer_lib
  from tensorflow_model_analysis.utils import model_util
  from tensorflow_model_analysis.utils import util
  from tensorflow_metadata.proto.v0 import schema_pb2
label_desc: Use image node_id 2 for calling the _ComputationsCombineFn obj's underlying member method code with example usage: obj.add_input(accumulator, element) and returns: tuple, item