class_docstr: A DoFn that extracts the metrics output.
code: def __init__(self, eval_shared_model: types.EvalSharedModel) -> None:
      super().__init__({"": eval_shared_model.model_loader})
  
      # This keeps track of the number of times the poisson bootstrap encounters
      # an empty set of elements for a slice sample. Should be extremely rare in
      # practice, keeping this counter will help us understand if something is
      # misbehaving.
      self._num_bootstrap_empties = beam.metrics.Metrics.counter(
          constants.METRICS_NAMESPACE, "num_bootstrap_empties"
      )
  
imports: from typing import Any, Dict, Generator, Iterable, List, Optional, Tuple
  import apache_beam
  import numpy
  from tensorflow_model_analysis import constants
  from tensorflow_model_analysis.api import types
  from tensorflow_model_analysis.eval_metrics_graph import eval_metrics_graph
  from tensorflow_model_analysis.slicer import slicer_lib
  from tensorflow_model_analysis.utils import model_util
  from tensorflow_model_analysis.utils import size_estimator
label_desc: Use image node_id 1 to create a new _ExtractOutputDoFn object from inherited base classes: model_util with example: obj = _ExtractOutputDoFn(eval_shared_model)