old_contents: from .estimators import *
  from .meta import *
  from .regression_model import *
  
  __all_estimators__ = [
      "ReplayMethod",
      "InverseProbabilityWeighting",
      "SelfNormalizedInverseProbabilityWeighting",
      "DirectMethod",
      "DoublyRobust",
      "DoublyRobustWithShrinkage",
      "SwitchDoublyRobust",
      "SelfNormalizedDoublyRobust",
  ]
  
new_contents: from obp.ope.estimators import BaseOffPolicyEstimator
  from obp.ope.estimators import ReplayMethod
  from obp.ope.estimators import InverseProbabilityWeighting
  from obp.ope.estimators import SelfNormalizedInverseProbabilityWeighting
  from obp.ope.estimators import DirectMethod
  from obp.ope.estimators import DoublyRobust
  from obp.ope.estimators import SelfNormalizedDoublyRobust
  from obp.ope.estimators import SwitchDoublyRobust
  from obp.ope.estimators import DoublyRobustWithShrinkage
  from obp.ope.meta import OffPolicyEvaluation
  from obp.ope.regression_model import RegressionModel
  
  __all_estimators__ = [
      "ReplayMethod",
      "InverseProbabilityWeighting",
      "SelfNormalizedInverseProbabilityWeighting",
      "DirectMethod",
      "DoublyRobust",
      "DoublyRobustWithShrinkage",
      "SwitchDoublyRobust",
      "SelfNormalizedDoublyRobust",
  ]
  
subject: fix flake8 error for ope/__init__.py