docstr: Load, but don't initialize, the BTB class which will be responsible for
  choosing non-hyperpartition hyperparameter values (a subclass of Tuner). The
  tuner must be initialized with information about the hyperpartition, so it
  cannot be created until later.
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code: def load_tuner(self):
      """
      Load, but don't initialize, the BTB class which will be responsible for
      choosing non-hyperpartition hyperparameter values (a subclass of Tuner). The
      tuner must be initialized with information about the hyperpartition, so it
      cannot be created until later.
      """
      # tuner will either be a key into TUNERS or a path to
      # a file that defines a class called CustomTuner.
      if self.datarun.tuner in TUNERS:
          self.Tuner = TUNERS[self.datarun.tuner]
      else:
          path, classname = re.match(
              CUSTOM_CLASS_REGEX, self.datarun.tuner
          ).groups()
          mod = imp.load_source("btb.tuning.custom", path)
          self.Tuner = getattr(mod, classname)
  
      LOGGER.info("Tuner: %s" % self.Tuner)
  
imports: from __future__ import absolute_import, unicode_literals
  import datetime
  import imp
  import logging
  import os
  import re
  import socket
  import traceback
  import warnings
  from builtins import object, str
  from collections import defaultdict
  import boto3
  import numpy
  from atm.classifier import Model
  from atm.constants import CUSTOM_CLASS_REGEX, SELECTORS, TUNERS
  from atm.database import ClassifierStatus, DBSession
  from atm.utilities import ensure_directory, get_instance, save_metrics, save_model, update_params
label_desc: Use image node_id 3 for calling the Worker obj's underlying member method code with example usage: obj.load_tuner() without return types