class_docstr: CombineFn which wraps and delegates to another CombineFn.
  
  This is useful as a base class for other CombineFn wrappers that need to do
  instance-level overriding. By subclassing DelegatingCombineFn and overriding
  only the methods which need to be changed, a subclass can rely on
  DelegatingCombineFn to appropriately delegate all of the other CombineFn API
  methods. The contract of this base class is that the functionality of
  combiner c = MyCombineFn(), will be identical to the behavior of the wrapped
  combiner d = DelegatingCombineFn(c).
  
  Note that it is important that this class delegate all of the CombineFn APIs,
  as otherwise the contract would be broken and calls to the DelegatingCombineFn
  would not be forwarded to the wrapped CombineFn.
  
  TODO(b/194704747): Find ways to mitigate risk of future CombineFn API changes.
code: def create_accumulator(self):
      return self._combine_fn.create_accumulator()
  
file_path: model-analysis/tensorflow_model_analysis/utils/beam_util.py
imports: from typing import Any, Iterable, TypeVar
  import apache_beam
label_desc: Use image node_id 3 for calling the DelegatingCombineFn obj's underlying member method code with example usage: obj.create_accumulator() and returns: self