class_docstr: Pull calculation based on reference mean and standard deviations
code: def transform(self, datastore):
      self.logger.info(
          f'Comparing "{self.assign_to_key}" with reference "{self.reference_key}"'
      )
      return super().transform(datastore)
  
imports: import numpy
  import pandas
  from popmon.analysis.apply_func import ApplyFunc
  from popmon.analysis.functions import expanding_mean, expanding_std, pull, rolling_mean, rolling_std
  from popmon.base import Pipeline
  from popmon.stats.numpy import mad
label_desc: Use image node_id 2 for calling the ReferencePullCalculator obj's underlying member method code with example usage: obj.transform(datastore) and returns: super