class_docstr: Calculates differentially-private l0 bound (i.e. max_partitions_contributed).
code: def _calculate_number_of_partitions(self):
      distinct_partitions = self._backend.distinct(
          self._partitions, "Keep only distinct partitions"
      )
      return pipeline_functions.size(
          self._backend,
          distinct_partitions,
          "Calculate number of partitions",
      )
  
imports: from dataclasses import dataclass
  from functools import lru_cache
  from typing import List
  import pipeline_dp
  from pipeline_dp import dp_computations
  from pipeline_dp.dataset_histograms.histograms import Histogram
  from pipeline_dp import pipeline_functions
label_desc: Use image node_id 4 for calling the PrivateL0Calculator obj's underlying member method code with example usage: obj._calculate_number_of_partitions() and returns: pipeline_functions