class_docstr: A Spark RDD counterpart.
  
  PrivateRDD guarantees that only data that has been aggregated 
  in a DP manner, using no more than the specified privacy 
  budget, can be extracted from it through its API.
  
  PrivateRDD keeps a `privacy_id` for each element
  in order to guarantee correct DP computations.
code: def _get_privacy_id_extractor(
      self, contribution_bounds_already_enforced: bool
  ):
      if contribution_bounds_already_enforced:
          # Privacy ids are not needed when contribution bounding already
          # enforced.
          return None
      return lambda x: x[0]
  
file_path: pipelinedp/pipeline_dp/private_spark.py
imports: from pyspark import RDD
  from typing import Callable, Optional
  import pipeline_dp
  from pipeline_dp import aggregate_params, budget_accounting
label_desc: Use image node_id 10 for calling the PrivateRDD obj's underlying member method code with example usage: obj._get_privacy_id_extractor(contribution_bounds_already_enforced) and returns: function, None